Don't respond with 500 when an unsupported format is requested

When Rails receives a request for an unsupported format, a
`ActionView::MissingTemplate` is thrown. This is why we catch the
exception and set the status to 406 Not Acceptable instead of the
default 500 Internal Server Error.
Merge pull request #41 from rbCAS/handle-unsupported-formats

Don't respond with 500 when an unsupported format is requested
rename css to scss so @import works as expected
added rake tasks to search users and deactivate two-factor-authentication
Merge pull request #42 from rbCAS/reset-two-factor-rake-task

added rake tasks to search users and deactivate two-factor-authenticatio...
check if two factor authenticator exists before trying to remove it
Merge branch 'rails4' into handle-broken-service