Prepare package for npm publish

This is related to #1049, makes the preparations necessary to prepare this package for release on NPM.

I have a build process that copies necessary vendor files to my "public" folder on build. All those dependencies are in NPM except this single repo, which I am forced to use bower for. There is also the browserify use-case that expects this to be an NPM dep, and if isn't would be the single required bower component.

Steps to release this repo onto npm:

1) Merge this PR!

2) Create or login to your npm user:
 - `npm adduser`

3) Publish Phaser, run the following from the base repo directory:
- `npm publish`

4) ???

5) Profit.

If you need any help, just reach out to me on gmail.

Thanks!
Suggestion: Use package.json `files` whitelist instead: https://www.npmjs.org/doc/files/package.json.html#files

(Maybe I should pr that to pixi also hah)