Backup Support

With enabling BACKUPSTEAMUSER (either directly in the Game Config or by adding the game to the Backup Steam Category) all directories with files from the steamuser inside the Proton pfx will be backed (using rsync) when closing the game. The destination directory is STLCFGDIR/backup/steamuser/id/$AID. A STLCFGDIR/backup/steamuser/title/$GAMETITLE symlink pointing to it will be created as well. Files and directories can be excluded from the backup, by either adding them into the per game STLCFGDIR/backup/exclude/exclude-$AID.txt or into the globally parsed STLCFGDIR/backup/exclude/exclude-global.txt exclude file. For easier editing both files are also available via the Editor Dialog.