Anti-aliasing for 3D rendering (NOT Ready for Merging)

This PR allows the user to specify the anti-aliasing for 3D rendering in TVTKScene. Inorder to maintain interactivity, anti-aliasing is disabled when the user interacts with the scene and re-enabled once the interaction is finished.

Current State: Works correctly with respect to user interaction.

Pending :
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1. Tests
2. Test if the observers are released properly
3. Code cleanup