Convert sidecar data files from JSON to YAML

[EvanLovely]

Let's move over to this format!

[EvanLovely]

This npm utility would be very helpful and we could use this command to convert:

json2yaml --recursive --save --depth 4 source/_patterns/

Give special attention to patterns using the Data Transform plugin, perhaps leaving them in JSON if needed. The goal isn't total conversion, just highlighting a different way we can do the data files.

Also, the extension .yml doesn't work, only .yaml does. I've made an issue for that: pattern-lab/patternlab-php-core#25

[EvanLovely]

OK, that PR's been merged and we can now use yml instead of yaml! Let's use the shorter as that's what Drupal uses and also PL's own config/config.yml.

Relevant PR: #15