please add trust-store integration for access to contacts

Currently the 'contacts' policy group is reserved because giving access to the address-book-app's DBus API allows applications to obtain all contacts without user consent. If 'contacts' are going to be made generally available to untrusted appstore apps, the address-book-app service needs to be modified to use trust-store, like location-service does. Integrating with trust-store means that when an app tries to connect to the address-book-app over DBus, address-book-app will contact trust-store, the trust-store will prompt the user ("Foo wants to access your contacts. Is this ok? Yes|No"), optionally cache the result and return the result to address-book-app. In this manner the user is given a contextual prompt at the time of access by the app. Using caching this decision can be remembered the next time. If caching is used, there should be a method to change the decision in settings.

Targeting to T-Series for now, since the trust-store is not in a reusable form yet.