Prevent proxying video content or block it

[jon-betts]

For: #249

It turns out we are proxying video content, which is a shame. We should either find a way to avoid this or block the video category.

It would be ideal if we could do this by using the mime type rather than listing sites. Some nice ideas:

• If we can stop the javascript from rewriting it in the first place that's ideal, but may require hacking wombat.js or passing a lot of data to it
• Failing that we might be able to catch the request on the back-end and put our own "rewriter" that redirects instead. This won't be as efficient but is better than letting it all through.

Blocking may require the blocklist work to have completed #239

[jon-betts]

The current behavior is actually already blocking in the same way as Via. I think going beyond that is probably a enhancement rather than a parity move, so we can delay it.

Also it looks really hard.

[jon-betts]

Yeah thinking about it, I'm going to call this done. And file an enhancement ticket instead: hypothesis/viahtml#23