Use Highcharts.Options type for ChartModel.highchartsConfig

[amcclain]

Would want to look carefully around any complexities with extra modules or things like that, but this would be a big upgrade over our current bail-out to PlainObject when it comes to getting help writing and updating chart configs.

[amcclain]

Ah - the curse of "quick wins" strikes again...

So we deliberately don't import HC at all as a Hoist dep, to make it clear that any project / developers wishing to use it must review and properly license the library according to their terms.