Bug Fixes, enhancements and more functionality.

Fixed a number of bugs regarding lost frames.
Introduced occlusion culling to improve responsiveness and free
resources. Introduced additional scripts for the training scene as well
as some enhancements. Finally, assets and resources were categorised in
a better more clear way.
Merge branch 'master' of https://github.com/raikky/EndoscopySimulation

Conflicts:
	Assets/Meshes/ObstacleSphere.prefab
	Assets/Meshes/ObstacleSphere.prefab.meta
	Assets/Scenes/simulationScenes/simulationSceneLow.unity
	Assets/Scenes/simulationScenes/simulationSceneLow.unity.meta
	Assets/Scenes/simulationScenes/trainingScene.unity
	Assets/Scenes/simulationScenes/trainingScene.unity.meta