The UI is now on the page, meaning there is no popup. All code in src/popup has been moved to src/content.
The UI can be opened in three ways:
A) Clicking the extension's button in the browser (clicking again will close it)
B) Clicking the ◀ icon (clicking the ▶ will close it)
B) Clicking any "+" add section button (this will always force it open)
The UI's state (either open or closed) is written and read from storage for continuity
This PR introduces a few things: