Fixup signin and signout

No Issue
- Move authentication related handlers to the Application route.
- Switch Sign Out from a button to a link.  Use the signout route
  to handle invalidating the session and redirecting instead of
  an action from a button.
- Clear error messages on signin page when pressing log in button.
- Errors are now always shown on sign in screen and a success
  notification is shown after sign out.
- Update functional tests.
Merge pull request #3447 from jaswilli/auth

Fixup signin and signout