Implement service worker support for IPFS

[bmann]

I'll start with the big part. IPFS Companion is a browser extension. Extensions run in the main web UI thread. Service / web workers run in their own thread.

To improve performance of Drive, we could implement a service worker version of IPFS running in the browser.

This would not be compatible with IPFS Companion, so this means dropping support for IPFS Companion. It has about 20K installs and lets users run a local IPFS node.

Since we focus on making our services work web native in all browsers, even if they use some cutting edge tech, relying on extensions isn't in line with our goals.

The problem is that we need a separate ipfs daemon in every webpage. So, performance when running multiple apps / across multiple domains may be an issue.

Relevant discussions from IPFS land:

• The Future of "accessing API of remote IPFS node" ipfs/in-web-browsers#137
• https://github.com/ipfs-shipyard/service-worker-gateway
• Progressive P2P Web Apps (PPWA) https://gozala.hashbase.io/posts/Native%20talk.html

[icidasset]

Some more context on why I think service workers are not compatible, or bad for performance, in regards to IPFS Companion at the moment:

• We send a request to some (possibly non-existent) url which is intercepted by our service worker
• Service worker COULD now contact the main thread to use IPFS Companion, but this would block the main thread. Because, the ipfs stuff is performed on said thread.
• Another thing I imagine would be troublesome, is the transport layer between threads. I don't think you can do streaming.

[icidasset]

Superseded by #105