Sync status overlay for account avatar listing

[Rello]

The tray icons aggregates the status of all connected accounts. If one account is on warning or error, the tray icon will change to the corresponding warning or alert icon.

If there are multiple accounts connected, it is cannot easily be shown which account is causing the error and they need to be clicked one by one.

Request:

• for a sync status != ok, the corresponding icon should be shown as overlay in he account list
• the existing icons should be used
  • https://github.com/nextcloud/desktop/blob/master/theme/colored/error.svg
  • https://github.com/nextcloud/desktop/blob/master/theme/colored/pause.svg
  • https://github.com/nextcloud/desktop/blob/master/theme/colored/offline.svg
  • https://github.com/nextcloud/desktop/blob/master/theme/colored/warning.svg

The position of the icon is not decided and should be proposed as part of the change.