allow recombine, transfinite and embedding constraints on GModel entities
in parser

- fixed missing getShapeFunction/getGradShapeFunction + return all sf
  at once so we can implement MElement in term of these consistently
  (w or w/o FunctionSpace)

- can now merge multiple meshes and remove duplicate mesh vertices
  (useful e.g. when merging several STLs)

- added easy interface to create model-based postpro datasets on the
  fly + use this for mesh quality stats

* no lc at points == MAX_LC (-> lc/10 like for STEP & co)
* don't specify a char length at points by default when creating a geo with the GUI

corrected bug for higher order mappings in post views (supports q up to 4)

****************************************************************
**** PLEASE TEST YOUR SCRIPTS (ESPECIALLY ONES WITH LISTS, *****
****        COMPLICATED AFFECTATIONS, ETC.)                *****
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orientation in extrusions

* removed unused stuff (more to come)
* moved remaining into Common