add bar chart support to echarts and stylo-pie-table

[EvilDrW]

🏆 Enhancements
implemented rudimentary bar chart in echarts (because i wasn't able to use the nvd3 bar chart from within stylo-pie-table). expanded stylo-pie-table to have a choice of using bar or pie charts for drilldown-to-table.

[followbl]

I think the one thing we should just make a determination on is if we're going to be doing named vs default exports - named is usually better for debugging and stack traces - but obviously we should stick to a convention as a team

[EvilDrW]

I think the one thing we should just make a determination on is if we're going to be doing named vs default exports - named is usually better for debugging and stack traces - but obviously we should stick to a convention as a team

i don't have an opinion on this. i used default because it seemed to be very common in the superset-ui code. if you'd like me to change it, just say the word.