Update Highcharts Library

We currently have a warning in the Reports Status page saying that we should concider installing the library files locally.

Here is the full warning message:

Highcharts Library

Available through a CDN You are using the Highcharts library via a content delivery network. It is generally considered better practice to install the library files locally. Please see the README file inside charts_highcharts for instructions to install the library.

This is something that should be looked at after the migration is done.