Improve permalink navigation

If a user taps on a permalink (to an avent, a room, a user or a group), we currently erase the current navigation stack in order to display the requested screen on the top of the HomeViewController.

We should improve that and pop the new screen to the current navigation stack. The user should no more lose what they was reading.

Use cases to fix:
- [ ] Open a room or event permalink room the RoomVC
- [ ] Open a user permalink from the RoomVC
- [ ] Open a group permalink from the RoomVC
- [ ] Open a permalink to a room that is already in the navigation stack

Other use cases to think about:
- the user taps on a notification
- the user taps on a permalink outside the app

Start by tracing how permalink taps currently reach the HomeViewController and replace the navigation stack, then follow the listed room, event, user, and group use cases. Verify behavior for rooms already in the stack, notifications, and links opened outside the app; done means the existing navigation context is preserved while the requested screen opens correctly.

Written by the indexing model from the issue text.