Updated Usermanual and NSIS script

According to issue 28 (https://github.com/Daenyth/Cockatrice/issues/28) there were some changes in the prerequisites, so I set up a fresh VM with Win 7 SP1 (no other updates or installations), updated some URLs and applied changes to the usermanual.
The largest change was the MinGW setup and a minor change was an update to Qt 4.8.5 from 4.8.4 (which forced me to update the NSIS installer). Otherwise there were no differences.

I found one problem though: neither oracle.exe nor cockatrice.exe from this build+installation was executable in my fresh VM but if someone can reproduce this, this should be another technical issue.
This could be a compiler issue (g++ 4.8 seems to break some apps due to optimization) or because I didn't activate the Win7 installation for this test (which denied me to even change environment variables) and except the minor update in Qt the base libraries stayed the same.