Provide statistics view mode: histogram

[breznak]

If we move from "displaying the data" to "exploring the data" (do we want that?)

It would be useful to be able to run some "different views"/statistical modes on the data:

• a button "Histogram" opens a new window/view
• it takes the data from the current "scene" (selected series, zoom, scaled)
• compute a histogram on it
  • eg. vega can do that: http://vega.github.io/vega-editor/index.html?mode=vega-lite&spec=histogram