Bug 843889 - Delete StubActivity.
Bug 843889 - Factor CursorDumper out of RepoUtils.

This creates a new high-level package, org.mozilla.gecko.common.  I
intend org.mozilla.gecko.common to be code common to all (most)
Android background services.
Bug 843889 - Factor Tab out of TabsRecord.
Bug 843889 - Move Android Sync-specific Tab JSON manipulation into TabsRecord.
Bug 843889 - Move Tab into org.mozilla.gecko.db.
Bug 843889 - Move FennecTabsRepository.tabFromCursor to Tab.fromCursor.
Bug 843889 - Separate Sync-specific TestTabsRecord out of Fennec-exercising TestFennecTabsStorage.
Bug 843889 - Move TestFennecTabsStorage to org.mozilla.gecko.db.test.