Fixes#16165
All the logs about `settings_notificationsGetExPersonalMentions` are only to populate the model in the Notifications settings view, so it was pointless to load them on app start.
Now we lazy load them on loading that page.
An additional improvement that could be done later is to make it async and/or create a new API that gets all the DB info in one shot, because calling 4 APIs for each chat and community is a bit useless.
- signal for adding notification to the Activity Center introduced
and emitted, but that part is not handled within this commit since
there are some details needed to be discussed in the PR#5334
- signal for displaying ephemeral app notification is introduced
and emitted, but that part is not handled within this commit since
we don't have yet ephemeral notificaiton in place.
Fixes#4902
Jonathan Rainville
Sale Djenic