SkirmishControl: various improvement on Add Spring AI button
*No longer use UnitSync, instead will check for DataDir directory and current Engine directory. New Spring AI can be put in DataDir/AI/Skirmish and seem to work (at least in Windows. Still depend on Spring to acknowledge that the AI is there)
MinimapFuncBox.cs: Add Spring AI to regular Multiplayer AddAI button.
Note: the AI is indeed unstable. Haven't able to spectate a reliable game.
the Spring AI is not shown in main list, but at bottom of LUAUI AI, in subdirectory( hopefully doesn't look like something default)