Main menu

@kadst43 @AmbientOSX @ajiraffe 

Changes:
- Main Menu added
  - Main Menu is a scenario
  - Play Game button proceeds to intro screen scenario
- Render logic changed
  - `renderMode` determines what will be rendered, if anything at all
  - Nothing is rendered when videos are playing
- General purpose and useful functions moved to `source/utils.js`
- Fixed Version element style