Use Highcharts CDN instead of local copy

For the last 5 years, Highcharts has allowed CDN hotlinking. For more info, see this page:
http://www.highcharts.com/news/50-codehighchartscom-moves-to-cdn

The views_highcharts.make file should be removed, and theme/views_highcharts.theme.inc should be modified to pull highcharts.js from that location instead of a local file. This also removes the dependency on the libraries module.