Move Sprite's vertex data into a Mesh.

	- Mesh now handles setting up a VertexBuffer from an array or
	  FloatBuffer.

	- Sprite is now initialized with a Mesh for vertex data, rather
	  than maintaining it's own vertices and VertexBuffer.

	- VertexBufferTechnique now expects a Capable object to provide
	  a Mesh instance for initialization / drawing.

	- VertexBufferTechnique.Capable is now generic enough to be
	  merged into RenderingTechnique.

	- Vertices for Sprite used in HelloWorld test code, is now in
	  HelloWorld rather than hard coded into Sprite.

I like the idea of the Mesh class. Hopefully it will be a good way to
refactor code to share vertex data between instances of renderable
objects. As well as code for things like translation / rotation.