refactored cliff code for more readability
creation of cliff shapes to separate logical and graphical data
Terrain mesh is now divided in parcels for more perf
Shadows are back with higher resolution !
Map file doesn't contain anymore cliff info, cliff are found by comparing level diff and ramps.
    Map file is now very easy to paint
Cliff mesh and terrain mesh are now correctly linked
    Note that the terrain offset for equilateral facets may lead to clipped cliff's grounds. I'm looking for solution
Ramp work again, with raw cliffs for now