Add affiliation field / Backcompatibility (?)

[kferjaoui]

• Add space_group_number argument to latest version of jfjoch_client
• Replace Experiment class with an Affiliation drop down menu
• Treat measurement_tag as optional and omit it when empty to avoid double underscores

[kferjaoui]

This update of the epoc-utils relates to these issues in the GUI repo epoc-ed/GUI#208, epoc-ed/GUI#193

[kferjaoui]

⚠️ This PR breaks backward compatibility.
If we absolutely want to maintain that, then experiment_class needs to be restored. This would require:

1. revert 18922ae and a019c37 while keeping affiliation and usedAffiliations (look at the branch fix/keep-backcompat)
2. Duplicate or expose methods that build data directories using experiment_class (similar to how affiliation works below):

@property
    def data_dir(self) -> Path:

        # Directory where the current experiment will be stored.
        # Computed from the configured experiment
        # TODO! Do we need the support for a custom directory

        path = Path(self.base_data_dir) / self.affiliation / self.PI_name / self.year / self.project_id / self.today
        return path
    

    @property
    def work_dir(self) -> Path:
        # Directory where output of data analysis will be stored
        path = Path(self.base_data_dir) / self.affiliation / self.PI_name / self.year / self.project_id
        return path

@erikfrojdh or may be you have a cleaner solution?