cut down d3 v4 to used modules (for maintainability and startup speed)

[bernhardreiter]

D3 V4 ist modular, so instead of using the full import we can cut it down
https://github.com/d3/d3/blob/master/CHANGES.md

Value gained: better maintainablity because it is better understood what the code is supposed to do.
(maybe a bit of code reduction that needs to be loaded and executed, so could gain startup speed)

D3 is supposed to be used for chart in the Statistic view.