Initial qutebrowser support

[glacambre]

Closes #1190

[toofar]

I got it to load on a test site (because all the sites I care about have properly restrictive content security policies that qutebrowser doesn't attempt to bypass) but it sits down in the corner and I can't exit insert mode.

[glacambre]

@toofar Thanks for trying this out (and congratulations for figuring out how to do it on your own!). Yep, there still are a few things to change regarding how the frame is inserted in the page, this is what I'm working on at this very moment :).

Regarding CSPs, I think the most restrictive ones will remain an issue for Firenvim - the only way firenvim can work on fancy text editors is by inserting dynamically-genereted javascript in the page :/.

[glacambre]

@toofar The iframe should now be correctly placed over the textarea and qutebrowser should enter passthrough mode automatically. There's still a few tweaks I want to make, tests I want to perform and refactorings I want to do, so things aren't 100% done, but feel free to report other issues you might find :)

[hirotasoshu]

@glacambre Hi! Any updates on this?

[glacambre]

@hirotasoshu Nope :). I've been pretty busy with other things and haven't had time to even work on the most important issue I have to tackle yet ( #1193 ), so qutebrowser support is unlikely to happen for now. Sorry!