[EPIC] Harvard Gazette features to document/abstract out

I went through the codebase and identified the features I felt we were most likely to need for other projects. Some could be added to [`block-editor-components`](https://github.com/humanmade/block-editor-components) or [`hm-gutenberg-tools`](https://github.com/humanmade/hm-gutenberg-tools), some could be abstracted to a reusable block repo, some just need documentation.

Components:
- Look into the media select component from `block-editor-components`, is there anything to upstream from the Harvard media selector?
- Same for the custom render appender button
- Color palette picker - how does this compare to the section color in core?
- Primary category

Helpers:
- Max word count
- is-style

Templates (maybe not to abstract out, but just add descriptions):
- De-duplication
- Supporting content

Blocks:
- Accordion/accordion item
- Carousel
- Featured articles
- Image scroll replace/immersive (something with the scrolling of one item over another)
- Mega menu (compare to changes in core and other sites)
- Stats
- Tabs (compare to other sites)

Plugins:
- I seem to remember wpcom-thumbnail-editor was outdated but we used it anyway because it was the closest solution to what we needed? Did we make changes that we could upstream or fork?