Add an indicator to show that resources have been loaded over IPFS

[da2x]

1. Install IPFS Companion extension.
2. Visit a website that loads some resources over IPFS (like https://www.ctrl.blog).

Expected: There should be an indicator to show that some resources on the current page have been loaded over IPFS. The page is loaded over HTTPS but some static assets are served from an DNSLink enabled subdomain.

Actual: There is no visual indicator.

Notes: I'd normally suggest fixing up the pageAction icon, but browser support for pageAction isn't all that great compared to browserAction. Maybe just change the color of the browserAction icon? Attaching a green version for this purpose.

[lidel]

Subresource requests are easy to detect: ResourceType !== main_frame, and parent page is in request's documentUrl/originUrl (Firefox) or initiator (Chromium), so we have means of counting them per page/tab.

I agree, UX will be the tricky to get right, especially on Chromium browsers where it is not possible to show pageAction and browserAction at the same time.

What if we stop displaying peer count on the badge, and instead show the number of redirected resources on current page? (if any)