ActivityDefinition InteractionType

[ghost]

This PR contains the commented change suggestions from #17

[yingbiao]

I am wondering when this PR will be merged into master? We need this feature to get choices from statement.

[brianjmiller]

Prioritization of work on the OSS libs is difficult, I hope to have a chance to put time into the open PRs in the next couple of weeks. It will speed up the process of PR review if you rebase the changes to the current master branch, make sure you are only including the required changes to get to functionality, and make sure there is no backwards incompatibility in either code changes or other repo items. Submitting a "clean" PR will prevent delays in back and forth.

[reedmclean]

Like @brianjmiller said above and I mentioned over on #34, this commit history is pretty messy and it has a lot of changes that aren't relevant to the core intent of the PR.

A lot of what I requested over on #34 is also applicable here. Since this PR is about extending ActivityDefinition, please take a look at the commit history and take out changes that aren't relevant to that work. My guess is that you only need the changes included in a6d2264 and 603a702.