Added possibility to launch single play game for any doom port supported standard doom
command-line parameters - Single Play Tab. Just add required source port to the list and configure game parameters.
The configurations may be saved and used in the future.
Changed the way of Skulltag testing versions downloading/launching: all binaries are downloaded and installed
in the one predefined "Testing" subfolder, so its possible to configure and use common user files
(configs/skins/etc..) with all testing versions.
Testing archives don't deleted and can be used later instead of downloading (its possible to put them
there manually also)
It is possible to turn off autoloading of testing versions, in this case ordinary Skulltag client will be used
(Options - Game Launch Parameters)
