* feat(keyboard-shortcuts): show help in a react dialog

- Move shortcut help dom declaration to a react component
- Let open/close logic be handled by AtlasKit Dialog
- Remove static html for help from index.html
- Consolidate keyboard shortcut css

* squash: use lozenge for key styling

* squash: use different iteration style

* squash: update package-lock for lozenge

left blank in default meet installations, to be overridden by adding <base href="CDN_URL"> to /base.html