Notification: Improve false push handling

Push notification service mechanism forces the OS to display a notification even if we do not want.

But with matrix, we can receive push for events we do not want to display to the end user. There are technical events like call ice candidates but also e2ee events that are all pushed to the app because the server knows nothing about the content.

For the moment, we have no technical solution to prevent the display of such notifications. We do some cleaning afterward on next notifications but it looks hacky.

We will experiment the behavior on real user accounts with the TF 0.12.0. We will see if can at least improve the UX.