Reformatted user registration and login.

- Redesigned layout of login and registration forms to be more responsive.
- Enabled login with email (instead of username).
- Allowed users to create their own password at registration.
- Eliminated unnecessary form fields in registration.
- Increased size and visibility of form fields.
- Edited post-registration email to reflect changes in registration process.
- Required login to view content on commentaries page.
- Fixed broken images on some pages.
- Fixed extra padding in top banner on tablet-sized devices.