User page improvements

The error will not appear red *yet* because #2558 has not been merged. If we merge both, in either order, the error will be red on production. If it helps, I can also rebase this branch against master after #2558 lands, so that the error appears red when this branch is checked out in Vagrant.

After logging in, the *Verification Sent* page appears, and I can't figure out how to work around it and see the registration page. Any tips?
FWIW, the actual regex that is used by Django (and there by the current solution as well as the future allauth version) allows the following characters: @ . + - _
This is basically a fault in the current system but I wanted to mention it now that we're here.