v0.4.0: JSONP multisource support (#42)

* Add multiple JSONP data sources, assuming all data comes from JSONP

* Add array version of data definition for improving the jinja2 template

* Fix bug in Highchart add jsonp url

* Apply multi-source JSONP code to highcharts

* Update inline comments for clarity and accuracy

* Update variable name to 'data_list' as per request for style consistency