Add PowerShell build scripts, version.vcxproj

Add PowerShell build scripts, version.vcxproj

Based on the sequence of commits to xenbus, add powershell scripts to
build the solution using the EWDK
version.vcxproj generates versioned files (version.h, xeniface.inf and
wmi.mof) using scripts/genfiles.ps1
Strips duplicated functionality from build.py toproduce consistant
builds between python and powershell.

Signed-off-by: Owen Smith <owen.smith@citrix.com>