Render PNGs on the Server with PhantomJS

Would like some input on this as it can probably be cleaned up.  Allows you to render an image on the server rather than relying on the client.

http://www.highcharts.com/component/content/article/2-news/52-serverside-generated-charts

Let me know what you think and I can make any suggested changes.

Also merging in here: https://github.com/michelson/lazy_high_charts/pull/129