integrate d3 general graph and popup component

[TeKraft]

• bugfix d3 timerseries component - handle values with no data
• d3 general graph and popup component
  • add point hovering (d3 voronoi) to d3 general graph component
  • add show popup button to test with csv example dataset
  • update API getTimeseriesData to receive all datasets with the same offering and feature id
  • update metadata models (d3 general)

[TeKraft]

added:

• avoid no hovering for only one dataset
  • issue https://github.com/52North/helgoland-toolbox/issues/98
• pointradius will be updated
  • issue https://github.com/52North/helgoland-toolbox/issues/97