Warn about "App folder" permission for Dropbox #1090
Description
When a developer creates the app credentials for Dropbox and chooses "App folder" instead of "Full Dropbox" for the permissions, the files will not be accessible by any other remoteStorage apps.
We should check if we can get the info from the Dropbox API which access level is configured and warn the developer, in case they chose the wrong type.
We might also want to make the info about this more explicit in the documentation.