Add a "not sure" option

[michbarsinai]

Which would allow users to answer "not sure" to a question, and then go through the interview twice, once assuming "no" and then assuming "yes" (or any set of answers). Final tags are the composition of resulting tags.

[eaquigley]

During the 9/10 meeting we discussed looking at TurboTax as an example for a workflow when a user answers "not sure" or "don't know". The user would be taken to another page that would explain in more detail what the question is asking, where they should find the information relevant for their dataset, and at the end say something like, "if you still are not sure how to answer this question, you can download the questionnaire to be able to come back to it after you find out more information to answer this question Yes or No."