Win32 build

These are some additions/changes to make building for Windows possible. Firstly, all changes are introduced with/within/in a "#ifdef WIN32 ... #endif" block (timehelper.h is such a block itself). So, nothing is changed at all as far as the other platforms are concerned. Using these changes, I managed to compile Hydrogen for Windows (and launch it in Windows 7), using the amazing MXE (M cross environment) and a mingw-w64 toolchain, from the warmth of my Ubuntu. With no sound and with a couple of problems (I only saw 1 column of the song grid! Where was the rest? Screenshots will be coming along with an issue shortly.). I will write down the procedure. Quickly applying more or less the same changes (coarsely, i.e. breaking the other builds) a couple of days ago I had successfully built Hydrogen in Windows using a prebuilt bundle of QT along with the mingw-w64 that built it. I may document this too.