Build QtWebKit with Mingw

I'm refering to
https://bugreports.qt.io/browse/QTBUG-35971
that is required as base for my problem.

The deprecated but required QtWebKit for GammaRay is not building with Qt 5.6.1-1 on Windows with Mingw by default.

Reason: Several times copied ICU files (headers) all around the archive, partially old (maybe deprecated), especially platform specific headers.

Solution:

1) Rename all "Unicode" folders
2) Create a Unicode folder in the WTF folder
3) Copy only WTF-specific header / cpp files into this folder, no original ICU files
4) You can now remove the folders from 1)

For the build you can use the Mingw 491 prebuilt ICU 53_1 dwarf 32bit devel from
http://download.qt.io/development_releases/prebuilt/icu/prebuilt/mingw/

It would be great to have a prebuilt mingw QtWebKit not only because of projects not changing to QtWebEngine but also because of
https://bugreports.qt.io/browse/QTBUG-42725 until you are able to offer a build of QtWebEngine for Mingw.