Improvements for all users:

- Selective synchronization is available behind the
  `settings.partial-desktop-sync.show-synced-folders-selection` flag.
- The core of the synchronization process can handle selective
  synchronization without flags (only the configuration of the selective
  synchronization remains hidden behind a flag).
- The selective synchronization flag is fetched from the remote Cozy for
  every use case.
- We fixed an issue in our synchronization process which could lead to
  unnecessary metadata updates.
- When the app's OAuth client is revoked on the remote Cozy, fetching
  the Cozy's flags and capabilities won't result into an error anymore
  and the revocation pop-up will displayed again instead of the generic
  "Synchronization impossible" status.
- GUI state updates will now be queued up to avoid having two close
  updates overwrite each other and ending in a de-synchronized state
  between the app's main Window and the systray.
- Most remote folder deletion situations should be handled and the same
  goes for remote folder exclusions as part of the selective
  synchronization.