Unhide CalendarContract apis

This exposes the set of apis necessary to unbundle the Calendar
app and sync adapters as well as allowing third party developers
to officially access the calendar provider. This is the current
final set of apis to expose, though changes may occur if we
discover new issues. The documentation and CTS tests are still
in progress.

Change-Id: If77f9a1d49a26725b44b1014e8d088be7ffbc707