Thoughts around template/plan-export version 2

[hmpf]

DMPT

Make natural keys for all things dmpt:

• uuid for Template, Section, Question
• question uuid + choice for CannedAnswer
• current choice uuid + transition for ExplicitBranch

Ensure sections are in sorted order in export: by depth, super section, position.

Plan

Link to uuids instead of ids in AnswerSet.data and AnswerSet.section

Don't export Answers.