[WIP] Convert examples to static pages

The following pull request fixes the following issues:

* Remove PHP dependencies
* Full grunt build
* Static examples generation

Now examples can be generated by `grunt examples`.
It outputs a static site into the `out/examples` directory. This directory can be distributed as a ZIP archive. It still requires a web server to properly load game assets but runs under every HTTP server.

The PHP build system has been rewritten to a grunt task.
Phaser is now generated by `grunt`.

I didn't add `phaser.js` and `phaser.min.js` to the `.gitignore` but it could be a good since it would prevent further merge conflicts.

**WARNING:** This PR is marked as WIP because there is still a bug I couldn't solve: assemble is unable to generate `examples/animation/spritesheet.hbs` and I don't understand why.