====== Small tasks ======

  * Optimize the SphereMesh and the BoxMesh to share shader, vertexbuffer and indexbuffer.
  * Add a method AddSphere to the LineManager3D
  * Create a FullScreenQuad geometry type
  * Add some static helper functions to the PhysicsHelper: create a sphere, a box, other stuff? + write a test for it
  * Add function that loads an image from a file to a terrain heightfield. Also add a function to quickly create a model from a terrain heightfield and a way to render it. (plain rendering no geomipmapping stuff or other)
  * Create an OptimizedDictionary. This is a class that at the same time stores a Dictionary and a List, storing the same items, but allowing both fast search AND for looping.