Lua MainCfg vars

This branch adds the following "dynamic" variables to Lua:

• spstage_start
• sstage_start
• sstage_end
• smpstage_start
• smpstage_end
• bootmap
• tutorialmap
• tutorialmode
• skincolor_redteam
• skincolor_blueteam
• skincolor_redring
• skincolor_bluering
• invulntics
• sneakertics
• flashingtics
• tailsflytics
• underwatertics
• spacetimetics
• extralifetics
• nightslinktics
• gameovertics
• ammoremovaltics

tutorialmode is a boolean indicating whether the tutorial is currently being played or not, while the rest are integer variables that can be edited via SOC; you may recognise a number of them if you are an SRB2 editing veteran, hah! (Though mind you, sstage_end and smpstage_end are edited only indirectly via their _start counterparts)