Fix Unknown Element Ownership

This PR fixes issue #3431. 

The element wrapper for "unknown" elements was not honoring the "isRevitOwned" setting passed by outer calls such as ToDSType. This was causing elements wrapped as "unknown" to be deleted from the Revit document when their wrapper was disposed. This affected wall reveals, roofs, and other elements as noted by users in #3431.

Merge:
- [ ] Revit2016
- [ ] Revit2014

PTAL (This is being merged now as a priority fix for 0.7.5, but still requires review):
- [ ] @DynamoDS/michelangelo 
- [ ] @pboyer