Bug 1081082 - [Contacts] [Data Refactor] Provide a convenient way for pr...

...oviders to get access to their 'contacts' datasore
this is pretty specific, will make all apps have the same format `Xprovider.gaiamobile.org/manifest.webapp`, I would remove that restriction, passing directly a manifest.

Later for easier use, we can extend this class to make just this adjustment on the way we ask for the DS.