Media Capture support

[weepy]

Hi - I was interested if Media Capture was possible (in particular for MacOS). Typically with WkWebkit there's issues with app sandbox and permissions (especially with Mojave).

[nothingismagick]

I just saw this today, might be interesting to keep track of:
https://webkit.org/blog/11353/mediarecorder-api/

[weepy]

so i tried to run the example - media capture appeared to work fine, but whether this works when distributing is another question. (?).

[nothingismagick]

See this issue:
#85 (comment)

[wusyong]

#266 is our initial impl. But still lack flexibility at the moment.