v6.0b2: Fixes matrix export bug

Fixed the following:

• Could not export matrix dependent nodes due to variable reassignment error
• CornerPin node would be deleted even if 'All' was selected.
• Roto node would be offset from other nodes.

v6.0b1: Refactoring Beta

• Massive refactor and code cleanup
• Will no longer install menu items automatically on import, you need to call cardToTrack.run()
• The main function for executing cardToTrack has been renamed from corn3D() to card_to_track_wrapper(). If you already have python objects for your camera, card and background you can call card_to_track() which takes those arguments.
• New functions!
  • corner_pin_to_corner_matrix() transforms a CornerPin with keyframes to and from points into a transformation matrix based CornerPin, leaving the to/from knobs completely free.
  • matrix_to_roto_matrix() copies any node's transformation matrix into a Roto node's matrix.
  • reconcile_to_corner() that takes 4 Reconcile3D nodes in a list, and returns a CornerPin.
  • reconcile_to_tracks() takes up to 4 Reconcile3D nodes in a list, and returns a Tracker with those Reconcile3D's converted to tracks.