add money velocity analysis

[brenzi]

See Fig 5 of our blog: https://encointer.org/charting-the-development-of-encointers-longest-established-community-currency/

• remove the "quarterly" in the labels
• use Excel as a reference for how to calculate velocity. This needs to be evaluated by cycle:
  • extrapolate the current commercial turnover to a year and divide it by the current money supply

Provide a plot and CSV with all the relevant raw and calculated data in the "internal" space

this plot should be public (and should be an embeddable component / iframe, i.e. for explorer.encointer.org)

easiest first approach:

• analyze monthly, not by cycle (as data is ready for this)
• money supply should be average of beginning and end of month