Walkmode g2 fix

[ataulien]

Reworked NpcAnimationHandler.

• Walking now works in G2, too
• Other walkmodes (Walk, Swim, Dive, Sneak) are available and functional
• Overall animation handling is now less rigid than before

Also fixes Dialogs not startable in G2, caused by NPCs being stuck in an invalid animation state due to the S_WALK animation missing. (Issue #287 )