WIP: Add a basic user settings page. 

Fixes #51. 
By default we don't want to accept some of these tokens; for instance, accepting `:encrypted_password` will save an encrypted string of a password into the database. What we actually want to accept is `:password` and `:password_confirmation`, which `Devise` will use to set the new encrypted password for us. A lot of these we'll take out, but I can handle that in a commit once the UX of this branch is complete and it's ready to be merged.