rework auth/reg forms and sheet

- Drop deform from angular app -- this was too confusing and strange
  and makes it harder to pull the front-end application out of the
  repository.
- Make the sheet much more attractive by tying it to the toolbar
  in a clearer way and toggling between "Sign in" and the close 'X'.
- Start to normalize the way errors are handled in form submissions
  on the back-end by offloading basic validation messaging to the
  front-end, removing the need to constantly re-render the forms.

Still to do: flash messages (#233)