Introduce a SetAnimation behavior node.

This commit also introduced a Walk and Stand component which
gets currently only used for defining animations. The intention
is that the walking speed will in future be defined in the WalkComponent
and that there are other components for hte other movment types like
swimmming and running.
Don't let the game crash when an skeletal mesh has no animation during the saving.
Merge PR #1462 by @flo - animation related behavior node