[Amibe] Add Mesh.merge
[Amibe] Let VertexInsertion work without MeshLiaison
[Amibe] Add EdgesCollapser (move code from BeamInsertion)
[Amibe] make EdgeProjector public and add some callbacks

Callbacks to track vertices merge from out side the
EdgeProjector class.
[Amibe] Mesh.getVertexGroup now return a modifiable map
[Amibe] VertexSwapper: do not swap immutable edges
[Amibe] remesh.py: swap more after afront

This help a lot on coarse meshes.