Change Single Player to "Skirmish" and support pre-defined missions/campaigns

[YokoZar]

The massive single player window will be a bit overwhelming for a new user to Spring. New users won't know what map or AI to select, or even what the different mods mean. We want someone who just installed, say, Kernel Panic from a package to be able to click a button for single player missions and have a list of good game setups to choose from, complete with graphical teasers and mission descriptions.

That way, I can tell someone "Hey, install Spring and Kernel Panic" and he'll then be able to figure out how to start playing without any help.