mesh repairing: integration of face removal/flip

Include multi-face removal as a new modifier for mesh repairing.

Open tasks:

• Find/write function that returns adjacent element to a given element and face
• Finish function to create primitives iterable
• Write function that calls remove_face to compute the set of new elements
• Assign ids and basis to computed new elements to apply the change to the mesh (@mspinola; support: @pgupta, @brgerhar)
  • IDs
  • Basis
• Update neighbours (once remeshing is done connections have to be recalculated and updated)
• Clean-up code
• Fix build errors
• Add unit/integration tests (support: @brgerhar, @webmanue)
  • Design example that requires face flips
• Code review