MapModel: add getters for random maps based on type, so that the mapContainer does not have to magically know how maps and separators are ordered within the model

fix for issue #186 ("Screen gets messed up when selecting Hand Drawn Map")

unbreak snowball

Ok, 20,000 was a bit much. Arbitrary multiplier that seems to shove things off enough.

MapModel: comments/docs, small tweaks

reimplement the quit engine+frontend keys

add ammoprop to enable to up and down buttons on for the touch interface

decouple current theme from map theme (fixes theme confusion bugs of last commit)

MapModel converted to QStandardItemList; separators fixed; changed used data format (human-readable struct instead of magic list) for map info in HwMapContainer (+ various small cleanups in that class)

MapModel, various cleanups. TODO/FIXME: QComboBox separator not working with custom models