Move to 64-bit build

We currently build and deploy as a 32-bit application. This is really not great these days, especially when after the official end of support for Windows 10 no supported Windows 32-bit OS will exist any more.

It also means that all native dependencies must be 32-bit, e.g. VLC.

One problem is the 32-bit only pptviewlib, but I'm not sure if that even still works (see #19).