Destroy all signers when campaign is destroyed.
Move external services features to users namespace.
Remove ability to sign up spontaneously.
Make external services feature only about sign in.
Replace Typhoeus with Excon.

For some reason, vcr doesn't detect the request body when hooking into
Typhoeus.
Have vcr match request body for successful validation.
Fix identify verification.
Style front page for tablets and larger screens.