[Wishlist] Support for a variable containing cloud drives root folders

Would be {DROPBOX}, {GOOGLE_DRIVE}, {ONEDRIVE} and {ICLOUD}
(ask on the support group for others)

For example: “{DROPBOX}\MyFolder\”

Could be auto detected for

Dropbox: https://www.dropbox.com/help/desktop-web/locate-dropbox-folder

Google Drive: https://stackoverflow.com/questions/13454508/how-do-i-find-the-onedrive-skydrive-and-googledrive-folders-without-the-api

OneDrive: HKEY_CURRENT_USER\Software\Microsoft\OneDrive
https://stackoverflow.com/a/29562190/2327946

Done in v9.2.