Added support for user feedback. refs #598

- Added modal for typing feedback.
- Added POST route to feedback as a tmp fix, since  BL 4.1
  decided to remove it (it would seem they've broken their own
  code by doing so).
- Changed feedback link to be an image due to inconsistencies with
  using css transform and MS transform.
- Added feedback mailer and controller to handle feedback form
  submission and sending of mails.
- Added empty conf for action_mailer in application.rb disabling
  sending of mail unless specifically configured.
- Still TODO: make feedback work for non-javascript.