Dropdown select Phaser.js version for exmaples

* This allows you to try out different versions of Phaser.js with the examples by pulling them in from github. Though the examples still work offline as well. So it will use the local copy of phaser if it can't access github. So that includes all git tags i.e versions and also the dev branch version. 

* query param examples ```&phaser_version=v2.0.4``` ```&phaser_version=dev``` ```&phaser_version=1.1.6```

Motivation: I wanted to open a PR showing that particle emitters don't work in the dev branch of Phaser and wanted to just link to the example, but it was loading 2.0.5 not the dev branch which is 2.0.6. So implementing a query param for loading a give verison of phaser just made sense. 

![screen shot 2014-07-08 at 22 16 34](https://cloud.githubusercontent.com/assets/705554/3516778/396d7490-06e5-11e4-9c6a-50f26a9215c5.png)

![screen shot 2014-07-08 at 22 17 27](https://cloud.githubusercontent.com/assets/705554/3516786/6e1cfd5a-06e5-11e4-8a32-6f9f74d6eb94.png)