Clean up the "VisualSessionModel" for archive/bookmark
After !344 (merged), some things stopped working.
Since we have a new SessionModel, it should be relatively easy to implement differently sorted versions (including pinning/archiving) of the same data.
I'll put this on %v0.6.0-beta.15 , but it's more like a nice-to-have than a must for that milestone.
Edited by Ruben De Smet