#22 #23 Incorporate conversion to require.js dependency manager

Changes file inclusion to work with require.js. This change is destructive and has orphaned the branch `dev-map`

Incorporate the following changes from `dev-map`
- [x] entities.js - changing game state to game over
- [x] main.js (now game.js) - add the following `me.state.set(me.state.BRIEFING, new BriefingScreen()); `
- [x] screens.js
 - Create BriefingScreen.js and include new code
 - copy changes from TitleScreen (actually, I should attempt to update all screens)