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.
This isn't actually necessary, not that it's in the way or anything, but it actually makes you type more than leaving it out would. You could just do `QApplication::clipboard()->setText(...)` instead.