Dispose of graphics resources deterministically.

Textures, FrameBuffers and VertexBuffers allocated by the Sdl2 Renderer were only being released via finalizers. This could lead to OpenGL out of memory errors since resources may not be cleaned up in a timely manner. To avoid this, IDisposable has been implemented and transitively applied to classes that use these resources.

As a side-effect some static state is no longer static, particularly in Renderer, in order to facilitate this change and just for nicer design in general.

Also dispose some bitmaps.
Clean up style of files affected by the last commit.
Made SheetBuilder rely on global settings rather than global renderer.

Additionally exposed an InitializeSettings method on game to initialize the global settings so that other classes can set up all the secret dependencies on the global settings required.
Merge pull request #6830 from RoosterDragon/dispose-renderer-resources

Closes #5116