Enable feat actions

[modawan]

We need to add support for feat actions in combat menus and game logic. All we have now are basic attacks.
Feats cannot be selected in chargen and level-up screens (see issue #4), so we need to implement console commands to add feats to characters.

[modawan]

#72 adds support for player characters to use feats. For now the implementation is just gameplay logic and visual. Mechanically all feats are identical to melee/ranged basic attacks.
AI is still unable to use feats, because script routines are not implemented yet.