Getting ready for production

[stormwarning]

• [x] Add Stylelint config
• [x] Move Django templatetags to new PyPI package
  see: https://github.com/l1f7/lift-balloons
• [x] Rename static/raw folder to frontend
• [x] Add placeholder images
• [x] Update JS module organisation ~- [ ] Update Sass partial organisation~ We can probably start using this without restructuring the Sass setup—that's going to take a bit more work.
• [x] Check out-of-date dependencies