Component refinements

[alex-ketch]

This PR has a whole suite of fixes, documentation refinements, and component fixes.
Storybook configuration has been updated to auto-import component documentation generated by Stencil.
I've also added fixed the ability to change component themes between Stencila and Material, as well as added Storybook Addon Knobs for allowing better experimentation with the components inside Storybook.
Right now there's still some unpleasantry that remains to be fixed, but I think they're better left for future PRs. They are around:

• the global CSS and how it interacts with the generated docs. Currently I've gone in and manually reset the conflicts with the Storybook UI.
• Changing between the Component Theme Modes doesn't update the view, you have to navigate to a different component and then back.
• Knobs have only been added to the Button component, with the intent to document other components in future PRs.

---

• feat(Button): Add styles for button anchor elements
• fix(Error): Fix incorrect component title in README
• docs(*): Include README in Button, CodeChunk, & Error stories
• fix(Tab): Remove stray style added for debugging purposes
• fix(ActionMenu): Fix rendering error when in Material mode
• chore(Deps): Update dependencies
• feat(Button): Add ability to render HTML elements as Button icons
• refactor(TabList): Render TabList from list of objects for more control
• feat(Button): Allow Buttons to trigger Form events across Shadow DOM
• docs(*): Fix incorrect component titles in READMEs
• chore(Deps): Update dependencies
• docs(README): Add CI badge to README
• fix(Button): Fix small and xsmall button style
• feat(CodeEditor): Add CodeEditor component
• refactor(CodeChunk): Extract CodeEditor component from CodeChunk
• feat(NodeList): Add stencila-node-list component
• feat(CodeEditor): Focus text editor when clicking empty space below it
• chore(Storybook): Add CSS Resource for just variables
• chore(Storybook): Autoimport component docs, fix theme switching
• fix(Style Stencila): Update theme font families
• fix(Tooltip): Don't style element being wrapped by Tooltip component

[nokome]

Thanks @alex-ketch ! I was playing with Designa's Storybook a few weeks a go so can appreciate the benefit of these changes! Looks good.