Some template and admin changes

Just some minor things I found while familiarising myself with the code.

Bootstrap changes
- Make navbar static, fixed isn't necessary.
- Fixed footer exceeding window height when it is fixed to the bottom.
- Tweaked user settings' grid sizes (lots of lg usage where sm is appropriate).
- Made admin forms more consistent with user settings forms; removed 'add' forms and just used edit forms for adding stuff - they were identical files.

Validation changes
- Fix being unable to add user via admin.
- Fixed admin validation to be done on both adding and editing.
- Added name validation for groups.