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.
Avoid calling QSettings from anything but `KVMainWindow` - I prefer having all settings-related code in one place, and having the main window tell other things about settings relevant to them.

As an aside, you don't need the brackets here, as you only have one statement inside them.