Added 2 concrete classes for towers
Added attribute "isBuilt" to towers
Base Tower
projectile instead of doDamage
some minor changes to tower
fixed merge
Remade to StateBasedGame, added a main menu
Revert "Remade to StateBasedGame, added a main menu"

This reverts commit 84ea6f519c2c52ebb662a89e3cc874d535a99b29.
Merge remote-tracking branch 'origin/Oskar'
Small temporary fix on Tower until Jonte is done