Report Windows OS names, not version numbers.

Fixes [issue #2](https://github.com/vidstige/Bugsense.WPF/issues/2).

All current Windows client OS versions will be reported using the product name they were sold under (e.g., "Windows Vista SP2", "Windows 7") instead of the OS version number (e.g., `6.1.7600.0`).

This code doesn't differentiate between client and server SKUs (e.g., Windows 8 vs Windows Server 2012) as that information is not in the OperatingSystem class, but only available by checking whether `OSVERSIONINFOEX.wProductType == VER_NT_WORKSTATION` (in `GetVersionEx`).