Fixed error checking in behavior so it happens before crash.
Added ability to create objects with behaviors, and made GameObject final to avoid accidental errors.
createBehavior now returns a reference to the created behavior, get returns it in the correct type, fixed docs in gameobject.
Fixed returns of createBehavior.
Fixed returns in the other createBehavior.
Fixed non-shared return type in Behaviors.get.
Fixed default materials
Merge branch 'release/v0.7.0' into develop
Merge branch 'develop' into feature/DropShared

Conflicts:
	source/components/behavior.d
	source/components/material.d
	source/core/gameobject.d