* Create a new table.
* Refactor NotificationFilterPreference so it could be easily stored in the database and can scale as well.
* Fix the UI.
* Add a cache for the new store.
* Adding a migrator.
* Enable the new mapping.
* Add test.
* Add functional tests.
* Make the results of the notification filter preferences livetable results predictable so tests are solid.
* Make saving messages in the UI more consistent.
* Adding a warning in the configuration file of activity stream.
* Remove the previous XClass.
* Remove the previous XClass's page during the migration as well.

XWIKI-15436: Stack Overflow when there is many notification filters.

* Improve the query.
* Add tests.
* Put inclusive filters BEFORE exclusive filters so that inclusive filters do not invalidate exclusive ones.
* Introduce the ConcatNode