Add snippet support and import SPL snippets

- Bump Smartdown to get Snippet support.
- Bulk import snippets from content doc
- Turn off (change the syntax) interpolation in snippets as unimplemented calculations will cause the page to error. Also turns off some answer interpolations as some snippets seem to reference answers that haven't been given (this shouldn't happen)
- Add a couple of outcomes, one plain (with conditionals) and one using snippets, as real-world examples
- This doesn't add snippets for all outcomes, as:
 - there are a lot of them
 - the content doc doesn't match the existing outcomes (some in one but not the other)
 - it's really hard to reverse an outcome to a URL to actually see it, eg find the right combination of answers.
- Adding more snippets to outcomes will happen in a future PR.