0030827: Add common functionality allowing to switch triangulation algorithm in runtime

0030827: Add common functionality allowing to switch triangulation algorithm in runtime

New classes BRepMesh_ConstrainedBaseMeshAlgo, BRepMesh_CustomBaseMeshAlgo and BRepMesh_CustomDelaunayBaseMeshAlgo are added.
These classes allow to add any custom triangulation algorithm to BRepMesh and perform post-processing and optimization of base mesh generated by those algorithms.
BRepMesh_Delaun: added possibility to process constraints when base mesh is generated by different algorithm.
BRepMesh_DelaunayNodeInsertionMeshAlgo: added PreProcessSurfaceNodes flag controlling addition of surface nodes (either before creation of base mesh or after) to gain maximum performance from triangulation algorithms.

Minor changes:
Use simple algorithm for cylinders when internal vertices mode is switched off to speed up computations.
BRepMesh_IncrementalMesh: added Perform method allowing to execute algorithm using manually created Context.