[Namespaces changes]

vert->vrt


clean up of some namespaces to comply the following naming:

Complexes (3 letters namespaces):
order 0 (point cloud    ) :vrt
order 1 (edge meshes)     :edg
order 2 (triangle meshes) :tri
order 3 (triangle meshes) :tet

Simplexes (extended namespaces):
order 0 (vertex)      :vertex 
order 1 (edge)        :edge 
order 2 (triangle)    :triangle (temporarily it remains "face")
order 3 (tetrahedron) :tetrahedron

vcg/complex/vertexmesh/base.h

@@ -57,7 +57,7 @@ People should subclass his vertex class from these one...
 #define __VCGLIB_VERTEXMESH
 
 namespace vcg {
-namespace vertex {
+namespace vrt {
 /** \addtogroup vertexmesh */
 /*@{*/