Favicon experiements

I am a programmer, not an artist, but here are some experiential icons
I whipped up.

They are only visible in the settings drawer when you add
`?experiments=true` to your site’s URL. Clicking on the icon will
change the favicon in the tab at the top of your browser.

For example you can see them at http://localhost:1337/?experiments=true
Merge pull request #32 from nightscout/rebase/settings

Favicon experiements