Fixes SwiftMailer exception reported by TravisCI

- Adds config to application container.
- Extracts SwiftMailer reference into application container at key, 'mailer'.
- Updates to TalkControllerTest to mock call to mailer send method.
Refactors to ForgotController to resolve mailer from container.
Merge pull request #144 from mdwheele/fix-switfmailer-exception-during-tests

Fixes SwiftMailer exception reported by TravisCI