change computation of vector at COG : average norms and directions separately; this allows to respect min/max

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add a metamodel defined tag to the default data base name; exclude the parameter WorkingDir from the database

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Warning : Points for high order prisms will change ! Old version is incoherent with what is done with other elements 

Goal: at the end, have only one algo for generation of Points/Monomials/Exponents/.. per element

new option menu for solvers (much simpler than in gear menu); needs to be enhanced with other actions