First zone (mostly) done! +minimap

While there was quite a lot of miscellaneous behind-the-scenes cleanup involved in formalising our first zone to explore, in the end, the only real visible distinction is that we have a new background illustration. Programming is cool! On the plus side we now have a snazzy new minimap, because I realised if I was having trouble remembering where I was in a floor players absolutely would also be having trouble.

Zones now have a small selection of "common enemies" which are present on every floor, along with a pool of "uncommon" enemies which are rotated in and out as you progress. Each floor selects one basic and elite mob from the "uncommon" pool to appear in standard encounters on that floor, changing up fights a bit as you move through a zone.

One detail that isn't implemented yet is the first zone's boss, but that will wait for a bit. Next on the agenda is the typical small smattering of assorting housekeeping and bugfixing tasks. Ta ta for now!