browserify-shim, gulp compile updates, and phaser 2.0 updates

First, thanks a bunch for publishing this boilerplate with the accompanying article as it has helped me learn about phaser :)

This pull request has a few things (sorry they aren't split up!)

  - switched to use `browserify-shim` instead of `napa`
    - I was getting errors when running the new phaser.js through browserify due to require functions in the newly included `p2` code
    - using this method instead means that the new CDN copy of phaser can be used and it will not go through `browserify` (no need as its already browser-friendly)
    - this is accomplished by adding a `<script>` tag to `index.html` to load phaser and a mapping of `phaser` to the JS global `Phaser` in `package.json`
    - faster downloading for users possibly!
  - updated `gulpfile.js` to use `vinyl-source-stream` and `browserify` directly instead of `gulp-browserify`
    - looking at the repo for `gulp-browserify` it shows the plugin as blacklisted. This was the recommended alternative
  - added uglify step to compile. 
    - It might make sense to do this as a separate task though to make debugging easier during dev. Do you have an opinion?
  - updated code to compile with phaser 2.0
    - created separate `game.js` to instantiate the `Phaser.game` as it makes things a bit less `this`-y when referencing `game`, also its the only way I could get the shim to work!)