* When running tests with VO2 measurements, it can be useful to see a
  graph of at least VO2 but also Ventilation to determine when e.g. a
  ramp test results in a plateau and can be considered done.

* Make the color of some VO2 measurements configurable.

* Add chart settings to WorkoutWindow, so that plots can be enabled or
  disabled. Also add the possiblity to do averaging.

* Use the term Ventilation instead of Respiratory Minute Volume

Move from using SeriesType from RideFile in order to allow more series
to be added without modifying RideFile.