[src][script] Enhancement of stbtel (local refinement)

Adding local refinement option in stbtel:

• changing original stbtel algorithm to detect polygon inner nodes by the inpoly bief function ;
• adding to stbtel_refine (and to converter.py refinement) an option to do a local refinement by using a GIS file containing (only) one polygon

Documentation has been also adapted and the test-case for local refinement has been corrected (the polygon for local refinement defined in the steering file was outside the mesh)

(this branch will allow local refinement with stbtel in Q4TS @jean-marie.kerloch)