Add issues basic line chart

Includes a working [basic line](http://www.highcharts.com/demo/line-basic) chart of the user's mood.

I know you [preferred](https://gist.github.com/akshatpradhan/2e083a092c4dcd1bdfd0/#comment-806998) the code to be different, but please take a look at this one. Doesn't it make the ChartFactory#build_chart method more readable?