Pain points with Joplin styling

I want to start documenting some of the specific pain points with editing Joplin styles in order for us to have a better path forward.

### Case Study: Publish Notifications

Recently, I had to add new templates for publish notifications. This is currently complex and widely spread out. There are multiple places where things must be edited:

- I wanted to create new templates. So I added them under `templates/Joplin_UI/messages` and `templates/Joplin_UI/pageStatus`. This made sense to me.
- They had corresponding js requirements, so I added them to `js/pageStatus/index.js`. The `js/` directory could probably be folded into Joplin_UI.
- Each .js file requires its own webpack loader at this point, and they must be individually added to `webpack.base.js`. And that new bundle must be added into the base template `templates/wagtailadmin/base.html`. We'd probably be fine just loading and running one bundle, like this company: https://tech.gadventures.com/integrating-react-into-django-5e6591097b9e
- Then I needed to add styling. I created some new files in `Joplin_UI`. But I also had to edit some existing styles for the edit page. Those styles appear to be spread out among `css/pages/edit.scss`, `css/editor.scss`, and `css/layouts/headers.scss`. This file structure needs to be better documented/organized/purged.

### What can be done?
- The structure within `templates/` is necessary in order to overwrite default wagtail templates.
- Everything in `js/`, `css/`, `Joplin_UI/`, and `templates/Joplin_UI/` are things that we have complete control over to re-organize as we need.