Sqlite storage

Start the foundation for the SQLite based panel data storage described in #188. This doesn't fully work yet, but I wanted to get feedback on the foundations before migrating all the panels. Some interesting points:

* All panels will use events to build their data.
* Panel data will be stored on every request in the `Dispatcher.afterDispatch` event. This solves a few problems around log files, query logs and view variables not reflecting data towards the end of the request.
* The debug kit database is initialized on demand by using the test db fixtures. This makes future 'migrations' a matter of simply deleting the sqlite DB and starting over.