Better Saver and Searcher compatibility

[h-0-0]

When Searcher has pointer to a Saver, ie. when we call 'searcher.check_existing_runs(saver)', the Searcher should keep the path stored in the attribute 'current_path' of the Saver up to date with the path corresponding to the last parameter configuration returned by the Searcher. That way the user can call '.get_current_path' to retrieve the path corresponding to the latest configuration given by the Searcher.

The above makes sense for existing Searchers (grid) and Savers (SaverCSV), however, this should really be implemented in a more abstract general way so that it will work for future Searchers and Savers.

To do this in a more general way there should just be some base method for all Searchers called 'update_state' that the searcher calls after each iteration.