MetricAggregator Model Refresh (Part 2 of 3)

.. the critical power models are now refactored to have a
   base class PDModel.

.. I have implemented the 2 and 3 parameter models as well as
   the veloclinic models

.. the ExtendedModel needs to be aligned

.. next steps are to put these values into a store and allow
   them to be plotted on the LTM charts.