Web simulator improvements

[pvinis]

• use uuid (fix(simulator-web): Use auto-generated UUIDs for simulated devices #682)
• hide qr code when we are connected
• dark mode for bg. autodetect, or maybe a toggle (fix: Show the navigation links on the web simulator page #684)
• check for update on mount
• figure out something for the site header links (fix: Show the navigation links on the web simulator page #684)

Addressed in #434:

• cycle through images
• make highlight color 7FFFD4
• re-fetch when the window gets focus again

[jbmorley]

Let's make the 'highlight' color #7FFFD4.

[jbmorley]

Let's unify the background color of the website and simulator too. Maybe we support dark mode in both?

[jbmorley]

How about automatically checking for an update when we start so the user doesn't have to initiate it?

[jbmorley]

Don't show the QR code when we know we've got an update. Perhaps don't show it until the initial fetch has failed so it doesn't flash?

[jbmorley]

Pretty sure we're not going to fix this bug all at once, so, while I'm thinking about it--I'd love to figure out a way to cleanly merge the navigation links from the top of the website with this. Or, at the very least, implement them twice, and style them similarly so you don't randomly get stuck in the simulator.

[jbmorley]

Maybe we can re-fetch when the window gets focus again? (I was switching between browser tabs)