Navigator: Show Projects after startup.

* Since migrating to Photon, the listeners of the IPersistencyService
  must be seemingly installed in the init phase. By that, the
  corresponding listeners are also aware of model loading.
* Also, remove an unneeded cast to avoid a warning.

Issue-Ref: 3540
Issue-Url: https://af3-developer.fortiss.org/issues/3540


Signed-off-by: Alexander Diewald <diewald@fortiss.org>