natural convection added in the incompressible code

Fixed intersection of metrics. Improved intersection of mesh metrics deriving from characteristic lengths.

bad parametrization can lead to bad results. Yte, this
implementation is FAST and, in the case of bad parametrization
optimization should be used 

* store max vertex/element number on a per-model basis (removed globalNum in MVertex/MElement). This should be improved, but forcing a GModel in the MVertex and MElement constructors

* use filename as a "partition indicator" in readMED (for both meshes and views), so we can deal with DDM datasets in MED (MED does not store partition numbers)

a frame solver is made
changed INRIA MESH output
removed feaure in BL field
started to do MNT diagrams