* CP-45071: Convert XenCenter build scripts to PowerShell.
* Removed obsolete variable.
* Pass the timestamp server and the certificate thumbprint as parameters to the build and sign scripts.
* Added further logging and made the verbose output of cmdlets optional.
* Updated README.
* Improved script readability.
Signed-off-by: Konstantina Chremmou <Konstantina.Chremmou@cloud.com>
