New optional boolean argument ("run") to gmsh::initialize(): if set, gmsh::initialize() will behave exactly like the Gmsh app, i.e. run either graphically or in batch mode depending on the command line arguments. Thanks @jonathan for the idea!

This allows to replicate the functionality of the Gmsh app with the API using a single function, which means that we will be able to replace the dynamically linked Gmsh executable with a simple Python script e.g. when ditributing Gmsh with pip.