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