Implemented LessonMetrics and logic behind measuring the lesson metrics
* LessonScalegrid2Position: cleanup touch/fft layer on new question, correct answers are visualized
  uppon correct submission
* added scalegrid-bsed support for chords
Added random switch for ScaleGrids and Degrees views.
Added "show only root position" switch to ScaleGrids view.
Take the "random", "show root only" or any button values of the
views above from the views directly. Not using notifications from views
any more.