New behavior node for playing (random) animations from a pool of animations..

Introduce a behavior node which can be used to play a random animation from a pool/list of animations. The new node also sets a new animationPool field of the skeletal mesh component, which will now loop randomly though the given animation pool once the current animation is done.

This pull request 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.