Use fk/select2-bootstrap-css@f263e899 to make select2 look better

Saves us a bit of trouble making select2 look good with boostrap. It does a
pretty good job, we just have to adapt a few things because we also don't
use bootstrap exactly as it is by default.
Fix missing string in rooms/invite_userid
Merge remote-tracking branch 'upstream/branch-v2' into branch-v2
Fix institution input in registrations/create

The select2 input was not being populated in registrations/create. So if there
was an error when trying to create a user, the form would show the institution
as a normal input, not a select2 input.