Windows MSI installers allow only one ParaView version to be installed at a time

With our NSIS-based ParaView installers, we could install more than one version of ParaView at a time. We should keep this capability, but the MSI installer no longer allows that. If you have an older version of ParaView installed and try to install a new one, you get an error message that says "Another version of this product is already installed. Installation of this version cannot continue. To configure or remove the existing version of this product, use Add/Remove Programs on the Control Panel."

We need to change the MSI installers to enable installing multiple versions of ParaView.