Added "normalized corner Jacobian" quality measure for triangles and quads (not yet used nor tested)

Test of metric as a shape measure. It uses the slot Rho instead of adding a new slot, define METRICSHAPEMEASURE in GmshDefines.h to activate !

Removed lots of warning introduced with my last commit, cleaned up a bit duplicateBoundaries, and introduced support for 2D for DuplicateBoundaries.

More cleanup is going to follow soon, especially in the modified part of commandline.

Addition of plugin DuplicateBoundary that allow one to modelize inter granular cracks with cohesive zones. 
Addition of the line command ComputeBestSeeds that allow one to optimize the placement of seeds in a microstructure to remove small edges from the Voronoï representation.
Small additions to cross3D and direction3D to compute the smoothness fo fields.

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New algo for packingOfParallelograms: the new points insertion depends on the local cross field smoothness

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prudently put between #if 0 #endif Those should allow
to produce better quality quad meshes and more robust
triangular meshes (random factor has disappeared) : 
Technically, the divide and conquer algo has been 
replaced by a bowyer-watson with robust predicates.