Bug 11522: improve formating of self-registration form

1. in prog theme, enable opac self-registration and inspect clear date
   with firebug; note that there are empty paragraph tags
2. add date of birth as a requirment in self-registration
3. apply patch
4. refresh page and notice that empty paragraph tags have been deleted,
   so that required lines up with clear date
5. repeat the above steps for bootstrap theme

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>