Update Highstock version from 1.3.9 to 2.0.3

- Updated the link to Highstock releases, since `http://code.highcharts.com/zips/` is not accessible anymore,
- Updated Highstock from 1.3.9 to 2.0.3,
- Changed the destination path from `webjars/highstock/<version>/js/` to the standart `webjars/highstock/<version>/`.