Add demo and story options to config file

[jakory]

Currently, the demo and story options for the game are hardcoded in, so if you want to change the mode of the app, you have to recompile and redeploy.

Add demo and story options to the config file, so you don't have to recompile and redeploy to get a different game version. It may also be worthwhile to add a start screen that lets you pick whether you want demo mode, story mode, etc when you start the game -- you can use the load scene function to pick the right one.