Hotfix/2390 Coach reports cannot compare across All facilities

Hi @aronasorman this fixes #2390.

It allow all facilities navigation in the coach report. 
The previous problem when we select the `all` facilities in  the drop down menu is that it always default to the facility as specified in the `config/settings/default_5Ffacility` in the admin.

We have modified the `coachreport/views.py` and removed the `facility_required` decorator to allow filter by All facilities in dropdown at front-end.
Rather than getting an empty queryset, why not just use `None`?