Smoother navigation across facility selection / coach report pages

Our coach report pages used querystring params facility_id/group_id/user_id.  However, the standard for the app is facility/group/user.  I've migrated the coachreports app to follow this pre-existing convention, which makes the interaction between require_facility and coachreports work more smoothly.

I've also dabbled in a few other things along the way:
* Make the coach reports header link add the relevant querystring args dynamically, if they exist
* Make the tabular view work when no group is specified
* Probably some other good stuff.