Add UseOIT flag to vtkRenderer

vtkRenderer now has a new flag (UseOIT) to toggle the use of the new vtkOrderIndependentTranslucentPass (OIT) for rendering translucent polygonal geometry. This flag is enabled by default which means the renderer uses OIT by default.

OIT is a newer approach to translucent rendering that yields better results without any performance trade-offs. However, this conflicts with other features of the vtkRenderer, namely MSAA based anti-aliasing. If you would like to use MSAA for anti-aliasing in a scene with translucent geometry, it is best to disable UseOIT.

The following pair of images show the use of this flag.

MultiSamples: 8, UseOIT: True	MultiSamples: 8, UseOIT: False
i.e. MSAA with OIT	i.e. MSAA without OIT