[x] level restrict train and build
[x] current tech gui
[x] tech bonus addition
[x] some tech effects
[x] tc and market trade
[x] age up menu
[x] end day upgrade on age up
[x] end day heal when on bld
[ ] bld ages upgrades
[ ] train problem
[ ] heal
[ ] convert
[ ] relics
[ ] tower diagonal constraint
[ ] tower defence effect -> new bonus type
[ ] castle
[ ] veterancy ranks
[ ] frenzy special case
[ ] gui production
[ ] gui train build
[ ] tech effects
[ ] unit tech requirement (paladin, champion, imp siege)
[ ] fsm back
[ ] undo

[ ] imp unit sprites 
[x] sprites stable, castle, uni, market, church, tower and bld upgrade

[ ] wheelbarrow doesn't work
[ ] search player by id, not by index