Revit Model Curve Creation in 2015

1) Use 2014 Revit SketchPlane creation method - effectively removing SketchPlane creation support in 2013
2) Extend ModelCurve unit tests to include unit conversion checks
3) New unit test for ModelCurve.ReferenceCurveByCurve
4) Fix AssemblyResolver failure for DSNodeServices when Dynamo is not installed

@ikeough