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.
Just a suggestion: it might be better to use "KCTViewer" rather than "Screenshot", to avoid naming conflicts with general-purpose screenshot applications.

Also, you don't need an arg for static text, you can do `QString("Screenshot %1.png").arg(currentTimeString)`.