Wait until both head and body are loaded before rendering.  Closes #2145.
When switching models, retain old one until new one is loaded.  Closes #2146.
Fixed seg fault, don't attempt to transfer joints between different models
(as opposed to different LODs).
Process geometry/textures in worker threads (via QThreadPool).  Closes #2137.
Indentation fix.
Merge pull request #2148 from ey6es/master

Various improvements to model loading: wait until head and body are loaded before rendering; render old model until new one is loaded when switching; process geometry/textures in worker threads.
make Agent parent of ScriptEngine so they stay on same thread
Merge pull request #2150 from birarda/master

make Agent the parent of its ScriptEngine
Merge branch 'master' of https://github.com/worklist/hifi into octree_server_scaling

Conflicts:
	libraries/shared/src/ResourceCache.cpp