HighCharts is not open source (#4383)

According to the (issue tracker of highcharts)[https://github.com/highcharts/highcharts/issues/4405#issuecomment-125124004] they do not consider the code open source. It's available for reading but that's about it.

The code is provided under CC-BY-NC via github.

See also:
https://shop.highsoft.com/faq#Non-Commercial-0