Focus on the next input element at various times.

A really trivial fix which saves users more time than you'd belive.
Focus on the user name box at login, the first first_name box when
registering users (or the last one if you've just added a row), or
the new_password field when activating.

Change-Id: I37f22cf67996c5d4cf089dceaf0a2295adfbbee6