add more robust error handling to user edit controller
add settings link to logged in menu, and signin spec helper
add user edit capability (read WARNING)

WARNING: As of this commit, authorization is NOT checked.
Any user (or even someone not logged in) can change any user's
information. DO NOT USE THE SITE AT THIS COMMIT IN PRODUCTION!

* add specs for successful user edit
  - log in user before performing tests
* minor modifications to user edit form
* add successful edit message and redirect to user controller