[work-in-progress] Smartdown version of register a birth

**Smartdown version of register-a-birth**

This work corresponds to the epic: https://www.agileplannerapp.com/boards/105200/cards/7983

**What does this contain?**

1. Write all the Smartdown for register-a-birth (including plugins)
2. Write all the utilities and rake tasks necessary to prove that transition in complete (in particular, comparison tasks)
3. Move scenarios to rake tasks so that they can be:
  - run independently for an individual Smartdown flow
  - stop breaking the build... use of global $imminence and $worldwide_api variables was making dynamically generated tests such as scenarios break horribly: for more details on the horror, come talk to me :)
4. Documentation on new rake tasks

If you want to take a look at the outcomes of the various rake tasks, please see:
https://github.com/camilleldn/smart-answers-metadata

**Future work**

Fix two bugs in Smartdown linked to the odd gsub behaviour in compare helper that is removed in the penultimate commit of this pull request
The two stories to fix them are:
- https://www.agileplannerapp.com/boards/105200/cards/9008
- https://www.agileplannerapp.com/boards/105200/cards/9009

**Still to do**

- [ ] run scenarios as part of test task
- [ ] add testing on combination generator, scenario generator and compare helper
- [ ] fix the Smartdown bugs mentioned above
- [ ] use the new Smartdown
- [ ] run comparison scripts without gsub hacks meant to ignore the Smartdown bugs mentioned above
- [ ] implement V4 changes (developer to time themselves doing it and document issues with the process :) )
- [ ] rerun comparison scripts
- [ ] document what a good transition process should look like
Rebase went fine :) :tada: