saved games directory discovery is incorrect

[DanAlbert]

(not urgent for us, just filing so folks are aware of it)

dcs-liberation/dcs_liberation#1116

dcs.installation.get_dcs_saved_games_directory has two problems:

• The DCS.openbeta is not tried (idk how to determine which should be used; I think standalone uses it but steam doesn't?)
• ~/Saved Games will not resolve to the correct location for users that have moved their Saved Games directory

In case anyone is confused by the second one like I was, Windows does allow you to relocate "shell folders" like Saved Games:

https://docs.microsoft.com/en-us/windows/win32/shell/knownfolderid would be a starting place for fixing the second issue. There doesn't appear to be a python API for this (though there are libraries on pypi), but it should be fairly easy to use via ctypes.windll.