Dynamo_Toolkit: Assemblies that reference Revit API are exposed but not handled

#### Description:

Methods coming from the assemblies that reference Revit API (e.g. _Revit_Core_Engine.dll_) are exposed in Dynamo, but cannot be used because as inputs they usually take Revit elements as Revit API objects that cannot be referenced by any means.

Dynamo allows interactive selection of Revit elements in order to "pull" them (see the .gif), however after pulling they are wrapped into Dynamo wrapper objects. It would be awesome if we could unwrap Revit API objects and allow calling Revit API dependent BHoM code directly on them.


An alternative would be hiding Revit API code base altogether, but it sounds like a bummer taken into account possible benefits coming from the above.

@al-fisher @rwemay @alelom FYI

Start by examining how Dynamo handles interactive Revit element selection and wraps the resulting elements, using Revit_Core_Engine.dll and the RevitAdapter example as context. Determine the design needed to expose usable Revit API objects or hide unsupported assemblies; done means Revit API-dependent BHoM methods can be called safely from Dynamo.

Written by the indexing model from the issue text.