Candera Behavior

Added support for Behaviors.

Behaviors have been added to support application development with considering the hierarchy of the scene graphs. Behaviors are small application building blocks that allow the user to create their own application handling. Being similar to Widgets Behaviors have the advantage that they can rely on hierarchical information, as every Behavior has to be attached to a node in the scene graph. By design they can be implemented in such a way that one behavior can even be reused for both 2D and 3D, if no special functionality of the Node below has to be used. Behaviors also support event handling through mechanisms for event routing (to other behaviors) and having a base interface (Behavior::OnEvent) to handle events.