Evaluate some of the tricker overflow design updates

[mackhowell-nava]

Follow up to: #3709

See comment:

Sometimes a list-and-loop affects only a subset of the questions in a section (e.g. 5D through 5G). How is this captured by the key?
Action item: investigate.

One of the proposed overflow page improvements is to group questions by section. Section data is not currently included in the key, but it seems straightforward enough to add that as one more attribute on each field.
Action item: investigate feasibility of this.

Another formatting improvement is to layout list-and-loop responses in a more tabular way.
Action item: investigate the feasibility of structuring the overflow data this way, as well as the feasibility of a tabular layout in prawn-markup.