Feature/key control import

Per [63879474](https://www.pivotaltracker.com/story/show/63879474).  Problem was traced to incorrect pairing of 1/0 to Key/Non-Key.  Was being imported correctly but rendered incorrectly to the user.

Also say that "key control" field wasn't being exported, which was due to non-basestrings being truncated to `''` non-exports; now non-`None`s are converted to strings for export.