Zone load tips

The game will now look in a zone's definition files for load_tips to display when loading a level of the zone, in that silly waiter titled Loading level... Load_tips are an exact copy of the ones in module definitions except they can't contain images. They also shouldn't be too long because the waiter looks silly too stretched.

At least the players have something to look at in addition to just "Please wait while loading the level...". As mentioned on IRC, they could be used for special zones (Caldera, dreams, Angolwen). For other zones, they might not be added at all or just contain a copy of the normal loading-game tips.

The PR doesn't include any load tips for said zones because I can't into ToME lore :P