Final changes before release v3.8

Change a condition in the flatpaks_installer.py script

Fix a bug with saving unencrypted periodic saving file

Remove unnecessary strings from GSchema file and add minor changes in…

… archive.py

Cleanup and UX improvements

Attempt to fix snapcraft.yaml

Update savedesktop.in

Fix a bug with showing self.switcher_bar on bigger screens

Update main_window.py

fix desktop-file-validate error

Replace ZipCrypto with AES256 and update release notes