Dropdown select Phaser.js version for exmaples

* This allows you to try out different versions of Phaser.js with the examples by pull it from github. Though the examples still work offline as well, so it will use the local copy of it can't access github. So that include 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 for this, wanted to open a PR showing that particle emitters don't work in the dev branch of the Phaser and wanted to just link to the example, but it was loading 2.0.5.