[C2] Rooms management (basic)

[ywarnier]

Add very basic support for rooms, so attendances can be attached to rooms.
We will later add the possibility to place them on a map, but for now we just want to be able to create and list rooms, to record where an in-person course (or any other event or thing) will take place.

The database structure already exists for this. We mostly need an interface to manage them and to add a configuration setting (maybe not even necessary) to ask whether we want to have them in all related resources' forms.

The interface should appear as a new block on the admin page, after the skills block. Use MDI icon floor-plan.

Rooms are linked to a branch (branch_sync table), so ther should be kind of a double management screen like for careers and promotions (the same section to manage both branches and rooms).

Then courses should have the option (in advanced params) to select a default room (in creation or edition forms), and attendances should offer the option (for each date) to select a room on creation or edition.

It should be possible from the room detail view page to see what uses that room (which courses/sessions) and when (which attendances of which courses/sessions).