Changing Server Communication from postTimestep to preTimestep

Some time ago we already developed a python based server communication for OGS with a specific test case with the building simulation software SimulationX. In the meantime we realized that the communication should better take place before each time step instead of after it, because the updated values will be used as (python) boundary conditions in OGS which will be used in the upcoming time step. When doing the communication before each time step we make sure that the updated values are used for the current time step.

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