Removable egos

Recently there was a talk on IRC how sweet would it be to be able to strip egos from an object. This achieves just that, keeping a list of egos at each object, too!
As a nice bonus, it showcases its capabilities by converting Imbue Item and Reshape Weapon/Armor to slap egos onto objects (and in the second case, to strip them from objects, too).
Randarts now have egos, too, and even randart stat powers are hoarded together by the name and converted into egos. Overall it's pretty sweet.
Of course, this is not limited to objects in its applications. Imagine: SHAPESHIFTING ACTORS.

Callback improvements

Some touches on the callback system:
- callback adding/removing is factored out so that the same loop isn't just written everywhere;
- priorities can now be specified for callbacks (default 0), callbacks with lower priorities get called first. (By a popular IRC request.) Of course this involves sorting but measures are taken to do actual sorting as rarely as possible.
(As a side-effect, callback-order is now well-defined, being sorted by type ("effect", "object", "talent") and implementing object (taking its .name or tostring()).)
- sustained talents can now be made to behave like passive ones in terms of callbacks, by specifying passive_callbacks=true in talent definition.

Fix UI left, right, etc. calculations

While working on statusbox, I've discovered that:
- absolutely everything dependent adds self.ix, self.iy twice. or thrice. this was masking top= bug, for example.
- right=ui sets right to ui.x, which usually sets an object flying to the opposite side of the dialog,
- top=ui sets top edge to be equal to the top edge of the ui, which is probably not what's desired (see left=)
- bottom=ui has similar problem to right,
- hcenter=ui sends a ui element flying half a dialog width to the right,
- vcenter=ui, likewise,
- and hcenter_left=ui I didn't understand what it's supposed to do.

This commit fixes all of the above, sans the last, and also adds 3 pixels of padding between everything to compensate for buggy yet sometimes desired previous results.

Redisplay fix

Calling redisplay() multiple times per turn is notorious for causing lag. The worst offender is probably Smoke Bomb, and it just got stripped from Creeping Dark.
This commit introduces a new scheduleRedisplay method, which uses little-known feature of game:onTickEnd to ensure that a redisplay would only get called once per this tick, not causing any frame drops.

LevelupDialog status box

Many users have expressed their frustration that appears when clicking too fast on a talent or stat to level it up pops up a message, forcing them to click "Ok". This commit adds a simple status line on top of the window, always clearly visible, that communicates these short messages in aesthetically pleasing colours. For important messages (e.g. the player somehow created an impossible talent loadout), the modal dialog usage was retained.

The status box displays short error messages instead of popups, to avoid
modal changes and user frustration.

Absorption cleanup

Currently, absorption shields are partially generalized, but there was still a wealth of absolutely identical code copy/pasted 3 times. This unifies on_damage and adjust_gfx into file-level functions to be consistent with the rest of the code there. Code relevant to spiked shields is also removed, because spiked shields are long gone.

This is the part of refactoring damage-connected code to be more consistent and modular.

actBase callbacks

Currently it's just a list of talent callbacks not being called callbackONActBase for some reason, This commit fixes it!

More callbacks

This one is extremely trivial: it adds a couple of callbacks that were requested over the course of developing "Callbacks engage".
This one is not vital in any sense, but bears some use for addons, particularly ones that do strange stuff with levelups.

Removal is done by rewinding an object and replaying all other egos on
top of it. Not too fancy, but surefire.

A lot of it involved renaming a single method in a talent definition.
Shrug.
Also talents now cool down after sustains are broken.

This one's to you, grayswandir76!

To do so, add a line:
	callbackPriorities = {callbackOnStuff=99}
alongside your callback definition. By default, the priority is zero.
All measures were taken to assure only a marginal slowdown compared
to previous behaviour.

Cleaned up Absorption (removed tons of duplicate code) and removed spiked code, as they no longer exist.

Fix ego stacking on randarts on certain egos

It's a long standing bug now that, due to the way resolvers work, applying the same ego of a certain type (e.g. robe of fire) to an item would make the statistic (e.g. resistance) on that item to spiral out of control exponentially. This branch fixes that by making it possible to resolve truly all resolvers before merging an ego.

It required some minor additions to the engine code, but nothing too brutal.
instant_resolve = "last" now runs last resolvers as well;
generic and genericlast resolvers now receive additional arguments
that are passed to resolvers.

Difficulty update

First time using the actual merge request feature, I might have done something incorrectly.

Just a quick update to difficulties that I've decided should be there regardless of what form the start zone rescaling takes.  The loss of stats on higher difficulties is very arbitrary and removing it helps simplify the ruleset which is good for balancing and player understanding.  Instakill immunity protects against a number of things that force turn skips, and absolutely nobody finds dying to Stone Touch fun or interesting.  Its just random and stupid.

Forced start zones allowing rares is almost certainly going to be a problem no matter how well scaling is addressed.

Newshop

Adds a lite/digger shop to Derth and the Iron Council.
Also added in the missing alchemist reference in the derth.tmx. No idea why it wasn't there.
Could use a new shop banner.

Shiftingparticles

Checked every instance of addParticles and addEffect to identify particle emitters that should use the new flag, and added it.

- Removed the instakill and rank changes for higher difficulties to normalize the ruleset