Provide unit conversions for all geometry types in RevitNodes

This pull request adds unit "awareness" to the geometry conversion layer provided by RevitNodes.

This pull request allows all ToRevitType() and ToProtoType() conversion methods (for Curves, Points, Faces, etc) to specify whether to convert from meters -> feet or feet -> meters, respectively.  Because only ProtoGeometry types are the only "user-facing" geometry types in Dynamo, all of this can be implemented in terms of those types.

UnitConverter.cs is the seat of this logic providing extension methods on all Autodesk.DesignScript.Geometry types (InDynamoUnits() or InHostUnits()).

Beyond that, this pull request adds:

1) Basic documentation modifications to improve visibility of these conversions
2) An minimal static assembly resolver in RevitNodes.  This does not utilize DynamoPaths in order to minimize the Dynamo dependencies of RevitNodes.  
3) ImportInstance is updated for this change and documentation is improved.
4) Basic unit tests for unit conversions - more to come.
5) A bunch of superfluous "fluff" comments were removed in various classes where the method was private and the intention obvious (i.e. private Autodesk.DesignScript.Geometry.Curve Convert( Autodesk.Revit.DB.NurbSpline does not need a comment)