Bump Smartdown to v0.5.0 to get Snippets
Add snippets to simple Animal example flow
Import SPL snippets
Disable interpolation/calulations in SPL

Replace %{}, which does interpolation, with !{}, so they're not run, but
we can still regex them out easily.

- None of the calculations are implemented yet
- Some of the snippets reference answers they don't _seem_ to have been
  given while getting to that outcome
- Add an example outcome using snippets

These aren't implemented yet
simple birth/nothing outcome, with conditional

These could be distinct outcomes, but the copy/intent is so
similar i'd like to keep them conceptually grouped for now.

It's easier to work with fewer (though slightly more
complicated outcomes) and split them out later
Merge pull request #1130 from alphagov/snippets

Add snippet support and import SPL snippets