2d meshing algo with -optimize does lloyd optim (tri or quad optim algo depending if recombine is selected)

* cartesian.h : new flag (simplex) in writeMSH to output the grid as simplices

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fix multiple cut

meshPartitionOptions::partitionByExtrusion assigns all extruded elements to the same partition as the source element

gui window

benchmarks.

Added comments and clarified class interfaces.

separate multistep, multipartition datasets)

matrices (and ask users to select 'Adapt visualization grid' first)