update docs (doxy), update operators (small fixes + add operator.discrete package), add profiler option (for memory), add testPoisson, + misc ... not finished, it may work ... or not

Cleaning tests (still failures in some operator tests). Cleaning and reorganising GPU. Fix advection and remeshing in pure python. Doc improvements.

Update of operators (continuous and discrete) : init and setup ok to fit with the new way to handle topology and discrete fields

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