experimental: propagate -setnumber/-setstring gmsh options to the onelab clients if they use the command line

there's no need to impose unique client names on the server: it just complicates everything - so let's remove this limitation

unregister client as soon as we mark it for deletion (trying to avoid skipping GMSH_CONNECT when the previous subclient is done but has not been deleted yet) 

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use global option db for PView options (needed to create new small new API: java C++ interface does not support std::string references !?)

geometry. It introduces subtle bugs when reading high-order post-processing views.

IMHO we should have an explicit command to do this, and not modify the mesh without
warning just by reading a file

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