Refactor to have a proper package

[BDonnot]

For example, why are the provided backend outside of chronix2grid ?

This is surprising at best

[BDonnot]

All imports need to be cleaned and improved...

For example, we cannot do:

from PypsaDispatchBackend.PypsaEconomicDispatch import PypsaDispatcher

It leads to:

  File "pypsa_loss.py", line 12, in <module>
    from PypsaDispatchBackend.PypsaEconomicDispatch import PypsaDispatcher
  File "/home/donnotben/Documents/chronix2grid_gaetan/PypsaDispatchBackend/PypsaEconomicDispatch.py", line 16, in <module>
    from .EDispatch_L2RPN2020.run_economic_dispatch import main_run_disptach
  File "/home/donnotben/Documents/chronix2grid_gaetan/PypsaDispatchBackend/EDispatch_L2RPN2020/run_economic_dispatch.py", line 25, in <module>
    import chronix2grid.constants as cst
  File "/home/donnotben/Documents/chronix2grid_gaetan/chronix2grid/constants.py", line 73, in <module>
    from PypsaDispatchBackend.PypsaEconomicDispatch import PypsaDispatcher
ImportError: cannot import name 'PypsaDispatcher' from partially initialized module 'PypsaDispatchBackend.PypsaEconomicDispatch' (most likely due to a circular import) (/home/donnotben/Documents/chronix2grid_gaetan/PypsaDispatchBackend/PypsaEconomicDispatch.py)