Update registration page

* Loop to render fields instead of using `form.as_p`
* Add ":" after labels using CSS
* Place fields side-by-side by adding `outer_class` to field widgets in `RegistrationForm` and digging down to retrieve them in the template
* Insert "Additional Information" header
* Preliminary SASS for styling
* Add `FieldErrorList` to build error message HTML

* No longer need JS code to add classes to the template output