Add mutators

* Add get/set methods to modify or retrieve GMSH geo parameters
  directly in the application source code.
Rename geo getters to feelpp standard
Merge branch 'develop' of github.com:feelpp/feelpp into feature/geomod
Merge branch 'develop' of github.com:feelpp/feelpp into feature/geomod
merge develop
Merge branch 'feature/geomod' of github.com:feelpp/feelpp into feature/geomod
fix last merge
Merge branch 'feature/geomod' into develop