Preparation for another alternative of unlocking premium features
Since it's now possible to provide paid content on Play Store in
Slovakia plus since some of the users don't have access to PayPal, we
provide another alternative of unlocking premium features.

GravityBox is not planned to be published on play store thus in-app
billing cannot be used. This means there will be another special
standalone paid app available on play store that will serve for
unlocking purposes.

This commit adds preparation for handling signature-based permission
protected broadcasts from unlocker app