Transaction support and a more or less complete rewrite of the

notification handling:

- Add methods to begin, abort and commit a transaction to DataStore.
- Add a QMutexLocker-like class for convenient transaction handling
  which aborts the current transaction when going out of scope.
- Use transactions for most commands that change the database, they are
  atomic now, ie. either succeed completely or don't change anything at
  all.
- Collect notifications during a transaction and emit them only if the
  transaction has been successfully committed.
- Add notifications for item and collection changes.
- Remove server-side notification filtering, it's not really needed
  since every item will be monitored at least twice anyway (by its
  resource and a search provider).
- Include resource and mimetype in the notification signals, allowing
  filtering by resource and by mimetype on the client side. This will
  be needed by resources and search providers.


svn path=/trunk/KDE/kdepim/akonadi/libakonadi/; revision=586785