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.
Oh, dammit, just me being stupid, if you do that it can't call the `finished()` handler because it's already deleted by the time the request finishes. Make it a Singleton instead then.

The way you're doing it there is the older, more complicated method, looks like I haven't updated the Viewer to use the C++11 method yet, see [here](https://github.com/KanColleTool/kct-tool/blob/master/src/KCTranslator.cpp#L14) instead. That's literally all you have to do - `static`s are thread safe in C++11.