* Fixed error happening sometimes when closing Zookeeper with non-default layers present

* Removed some verbose layer-related listener messages (mainly when removing layers)
* Fixed: If a layer that was previously referenced is somehow not found by Zookeeper it is removed from the list and a listener message is printed now instead of throwing an error message box

* Material editor pointer now received from global interface instead of being searched in scene. This will (hopefully) solve a rare error of medit not being found.

* Added code to prevent having bipeds inside templates during creation. Bipeds seem to throw all kinds of internal errors when ZK attempts to create them so, for now, they cannot be present inside templates.
+ Bipeds are represented using biped icon

Marsel Khadiyev (Software Developer, EPHERE Inc.)