Flatpak:
- Rewrite chat message deprecated logs : no more ensuring that this file must exists
- If a message history file exists in the application folder, let the SDK migrate data and remove the file
- Copy recursively all data from Flatpak installation, if files doesn't exist
- Split 2 migrations : old GTK and Flatpak
* Core creation in main thread but still async with timers
* For conference : no filter on items model.
* Remove conference storage and use directly the one that is in Core
* Fix calls model updates when a call become empty
* Fix missing functions
* Set Max Participants to 20
