unified class Incompressinle for 2d and 3D problems

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order 7->9 seem to be wrong : the way shape functions are
computed is maybe numerically unstable
 

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* the old code has been generalized to deal with these cases
* the new "in entity" boundary layer method(s) will not create a topology of
  "boundary layer entities" anymore, so this is superfluous

Added MElement::integrate, MElement::integrateCirc,
MElement::integrateFlux in similar fashion as in deprecated
Post/shapeFunctions.h

Integration of p-covector fields to riemann.

streamwise edge length is ok
functionIntegrator interface ok
functionevaluator with dgdof solution

recoded way to create boundary layers using explicit extrusion directions from vector post-processing view

direction and a distance. This require to have a method point in
Svector3 not very elegant but otherwise it's necessary to make cpp for
SPoint3 and SVector3

Several things for multi-constraint mesh partitioning + start circumscribed circle of MElement (need to be finished)

python interface: all std::vector<> in element constructors are declared as const, allows easy python binding