Add support for Highcharts accessibility module.

[uajqq]

Adds support for Highcharts accessibility module and suppresses a javascript console error.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[uajqq]

Since this repo is no longer being actively maintained, I've merged this fix into my own branch, which I'll maintain moving forward. Feel free to use it if you need this bug fix: https://github.com/uajqq/weewx-belchertown-new