Override default notifyChanges behavior

If there's the need to make different insert/update/replace queries, one would like to notify changes with `notifyChanges` only at the end of the whole process. As of now, changes are automatically notified at the end of each insert/update/delete.
By overriding the generated ContentProvider one could be able to override the default implementation.
Also, allowing the ContentProvider to be inherited from could let developers use some custom logic for join fake-Uris (which is something I'm doing) without having to manually edit the generated ContentProvider, by implementing that very logic in the inherited class.