Bugfix/remesh

[ylgrst]

This PR changes remesh.py:

• The remesher now works in case the user wants to remesh while keeping the boundary elements untouched, regardless of periodicity

• remesh_keeping_periodicity_for_fem has been renamed to remesh_keeping_boundaries_for_fem. To ensure backwards compatibility, remesh_keeping_periodicity_for_fem can still be called but raises a deprecation warning

• A new parameter has been added to remesh_keeping_boundaries_for_fem: if periodic=True (default), the remesher will check for periodicity before and after the operation (ie: the previous remesh_keeping_periodicity_for_fem behavior)

The relevant test has been added to test_remesh.py

[ricardo0115]

LGTM, just a small precision about what should we do when MMG is set to False.

Also is very important to note the change of this method name because it could lead to breaking retro incompatibilities issues in future Microgen releases.