Merge branch 'hotfix/0.3b.2'
Merge branch 'release/0.4'
[Core] Adds controller plugin "mailer" for interacting with Mail Service.

* removes ServiceLocatorAwareInterface from \Core\Mail\Message
  emails must be send either via controller plugin or mail service
[Applications] Refactors IndexController to use the "Mailer" controller plugin

* Fixes wrong settings key name in statusChange action.
Merge branch 'hotfix/0.4.1' into develop