Focus first textbox on all registration pages

When visiting a login, registration, or password reset page a person
will always want to start typing into the first textbox, so it makes
sense to embed the focus script into the base registration template.
Replace forgot_username.js with registrationBase.js

The functionality in registrationBase.js removes the need for a
specialized js file for the forgot username page.
Merge pull request #217 from azavea/feature/jcw/focus-first-textbox-on-registration-pages

Focus first textbox on all registration pages