[time-series chart]area chart style variation

[junlincc]

the new Echarts time-series chart looks great, but we should consider hardening it and increase time-series area chart style variation(Stack, Stream and Expand) to reach NVD3 area chart feature parity
after that, we can deprecate the old chart that has multiple issues not worth fixing
related apache-superset/superset-ui#799

Echarts - timeseries area chart:

NVD3 area chart:

[junlincc]

@willbarrett @nytai this can be good first Echarts tasks, what do you guys think?
https://echarts.apache.org/examples/zh/editor.html?c=themeRiver-basic
https://echarts.apache.org/examples/zh/editor.html?c=area-stack

cc: @rusackas

[willbarrett]

Let's see what shakes out after we get ramped up. This looks like a good candidate for the hardening phase in January to me, but we'll see what the rest of the team thinks!