kcms/notifications: Move per-event config into main page

Configure the notification events inline in the notifications settings of every application, instead of an external dialog provided by KNotifyConfig.

It adds a direct (optional) dependency to libcanberra to play the notification sound previews, but it was already indirectly dependent via KNotifyConfig.

Edit: After talking with @nicolasfella about this, we make libcanberra a required dependency instead of optional, and drop the Phonon path to play notification sounds.

As an added benefit, now the expected KCM behaviors for events (saving, restoring and defaults), are correctly implementing via a more handy KConfigXT EventSettings object.

Closes #68 (closed)

BEFORE	AFTER