Added kcm ui with global and app-specific config options.

Global options affect all notifications:

- Persistent only? --> Sync only notifications with timeout == 0?
- Include body? --> Add body string to summary when syncing?
- Minimum urgency

Per-application options affect notifications sent by a specific
application:

- Sync it at all?
- If yes, allow to define a "blacklist" pattern (QRegularExpression)
  to define which notifications should *not* be synced.

Applications are maintained in the per-device config and added when
seen the first time by the notification listener. From that moment on
they can be configured in the kcm ui.