Trigger dataChanged in timeline model on stateChanged in model manager

Allow the timeline model to clear its caches if the model manager changes
states. The timeline model caches for example event categories which
become invalid if the manager assumes the state EMPTY.

Task-number: QTCREATORBUG-10706

Change-Id: I10529ac56d39b169b850a8b5250fd36cb65a57ba
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Implement settings page for updater plugin.

Change-Id: I32cf1cd03413d59da99e99d0d6c19f6ba2bcc52f
Reviewed-by: Kai Koehne <kai.koehne@digia.com>