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.
Yup, most of C++ is really simple once you get it~
Especially in the standard library and core language, everything is just so insanely cleverly thought out. Qt's design is... less genius, some parts are just plain dumb and/or convoluted, but the language itself is incredibly good, and Qt's solid GUI systems make up for its occasional stupidity.