[PATCH] Cycle entities

[alpha123]

This patch allows quick selection of training buildings by means of keyboard shortcuts. For example, I can press J to select my first civ center, and J again with that CC selected to get my second civ center. Alt+J would select all CCs, and Shift+J adds them to the selection (Shift+Alt+J adds all CCs to the selection).

This patch has hotkeys for:

heroes: '
civcentre: J
barracks: K
fortress: Y
corral: O
market: P
stables: L
elestables: L
kennel: L
gymnasion: L
syssiton: L
armycamp: L
apadana: I
prytaneion: I