[Qt-creator] Add command prompt shortcut to windows install

[Leo Spalteholz]

I've been using QtCreator on Windows, and while the windows installer
bundles mingw and qt, it doesn't offer a shortcut to open a command
line with all the environment variables set to use those.
Like was mentioned earlier, QtCreator cannot compile every qmake/qt
based project, so we need some way to easily drop to a command line to
compile those things without having to set PATH and such manually...

That doesn't need to be in the IDE directly, just a link in the start
menu would be nice.

Cheers,
Leo