Create a structure to represent the interview logic

[nonprofittechy]

Right now, the interview order is just a list of strings. But ultimately in the output YAML, the author is going to add conditional logic to some screens. A list of strings doesn't work as well there.

Propose a simple tree structure:

["variable1", {"condition": "if x == 1", "children": ["variable2", "variable3"]}, "variable4"]