Add screenshoter

I think it's would be useful.
It's capture image from the webView widget, uploads it on imgur and copy to clipboard direct link to uploaded file. I checked it on my Arch linux and it builds and working fine.
My C++ and Qt knowledge is very low so code may (should) contain some mistakes. Any comment and fixes are welcome.
> Would work just fine.

Seems nope. Uploading function broke. I think because QNAM's parent is `this`?
I tried make `KVScreenshooter` singleton but I dont understand how it works and how it implement. https://gist.github.com/Yukariin/9991107908925e1bdb4a