- move code to load amari.kpi.LogMeasure -> kpi.MeasurementLog into
  load_measurements(). We will need to use that when showcasing E-UTRAN
  IP Throughput KPI to load another enb.xlog dataset.
- factor code to iterate over MeasurementLog and invoke kpi.Calc on each
  period into calc_each_period(). Same reason.
- factor plotting code into helper routines located only in kpidemo.py.
  The notebook version now uses those routines by way of importing. The
  plotting code is not helping to understand the KPI computation
  pipeline usage, so it makes sense not to show it out of the box in the
  demo notebook.