Treat functions as global that would previously be accessed through the GameFlow table. This does pollute the global environment in Lua a bit, but keeps it consistent with the functions in GameLogicScript, which are all accessed as globals.
Add some default member initialisers.
Remove WriteDefaults. Rename Intro to IntroImagePath and make it a std::string.
Add some documentation for the functions of GameFlowScript.
Fix some comments.
