Merge branch '1.6NPCDifficultyMisc' into 'master'

1.6 npc difficulty misc

(Difficulty)

- Most difficulty effects are now handled by birth descriptors

- Rares, randbosses, and fixedboss classes now start at set *player* levels, not NPC levels.  This lets us better align them with player power spikes like L8 talent unlocks and shops unlocking at L10.  Level rates are chosen arbitrarily based on how strong the base+class is expected to be and how late in the game the NPC is.  Most are in the 35-75% range

- Fixed difficulty fixedboss class scaling not actually working

(FIXEDBOSSES)

- Added classes to many bosses, its unclear what the start level should be so I mostly just set it to minimum level of the NPC.  This is likely to be hilariously wrong in some cases.  I think we should probably redo this to not kick in at any specific level and just use a low level_rate for lower difficulties, but lets try this for now

- Various misc updates, usually in the direction of making fixedbosses stronger across the board not just on higher difficulties.  I'd like to get away from the current model of fixedbosses almost never being where the actual difficulty spikes are

- Automatically activating sustains is now the default if the class is chosen randomly

- Recalculating ai_tactic based on talents is now disabled by default, but set to true if the class is chosen randomly

(MISC)

- Increased the level range of tier 1 a bit, there are 6+ of these and they barely scale

(POTENTIAL ISSUES/TODO)

- Forced start zones breaking with new numbers or not being properly updated

- Very little past tier 2 on higher difficulties has been tested much, no real reason to pre-beta

- AI kiting is likely too frustrating but lets wait to get full feedback on this
 
- Very little effort has gone into actually tuning the Sorc fight for the AI and difficulty changes


See merge request !515