Data structure supporting mesh analysis and modifications

The new class Poly_CoherentTriangulation (and the types that it depends on) is
added to the package Poly (toolkit TKMath).

This class implements the data structure and the API that supports analysis and
modification of triangulated mesh (like Poly_Triangulation). Possible areas
where this tool can be used:
   - Mesh generation and refinement
   - Mesh decimation
   - Constructions on surface meshes: offset, free boundary, geodesical, etc.

The data structure was optimized to provide the best performance of the
algorithms that would use it.
The full JAVADOC documentation is contained in Poly_CoherentTriangulation.hxx