#3486785 Adding preview functionality

Closes #3486785

• Implement Preview button in top bar
• In Preview mode show the current preview without the overlay
• Updated Hero component to have a hover state on buttons and a href so that it can be used for testing interactivity
• Render a new, minimal, top bar when in preview mode
• In preview mode, intercept all links and show a dialog instead.
• Swap Page data and Settings in left bar
• Settings tab is unavailable when there is no selected component
• Leverage Router to access the preview via /preview route and then control preview width with a /:width param.
• Move editor to /editor route
• Separate states to handle "disable overlay" and "show preview" so that, in future, we can disable the overlay via a keyboard shortcut
• I've actually added a "hidden" keyboard short cut ("v") that when held will disable the overlay and allow access to the iFrame. I'm leaving it in, even though it's buggy, because it's useful as a developer to have an easy way to inspect elements in the preview iFrame. It can be polished/developed further in a later MR.
• Tests for Preview mode