Release version 1.9.7

[BDonnot]

• [BREAKING] removal of the grid2op/Exceptions/PowerflowExceptions.py file and move the
  DivergingPowerflow as part of the BackendException. If you imported (to be avoided)
  with from grid2op.Exceptions.PowerflowExceptions import PowerflowExceptions
  simply do from grid2op.Exceptions import PowerflowExceptions and nothing
  will change.
• [BREAKING] rename with filename starting with lowercase all the files in the "Exceptions",
  module. This is both consistent with python practice but allows also to make the
  difference between the files in the
  module and the class imported. This should have little to no impact on all codes but to "upgrade"
  instead of from grid2op.Exceptions.XXX import PowerflowExceptions (which you should not have done in the first place)
  just do from grid2op.Exceptions import PowerflowExceptions. Expect other changes like this for other grid2op modules
  in the near future.
• [BREAKING] change the gridobj_cls.shape() and gridobj_cls.dtype() to gridobj_cls.shapes() and gridobj_cls.dtypes()
  to be more clear when dealing with action_space and observation_space (where shape and dtype are attribute and not functions)
  This change means you can still use act.shape() and act.dtype() but that act_space.shape and act_space.dtype are now
  clearly properties (and NOT attribute). For the old function gridobj_cls.dtype() you can now use gridobj_cls.dtypes()
• [FIXED] issue Indentation fault in backend.py to update_from_obs #561 (indent issue)
• [FIXED] issue Consistency of shunts_data_available #550 : issue with shunts_data_available now better handled
• [IMPROVED] the function to check the backend interface now also check that
  the topo_vect returns value between 1 and 2.
• [IMPROVED] the function to check backend now also check the topo_vect
  for each type of elements.

[BDonnot]

looks good (wait for tests to pass)