Code Review: Fix Silverlight builds

Add required Silverlight 3 and 4 runtime and SDK binaries so
Silverlight builds can occur without having those Silverlight versions

  • Adds a SilverlightSdkPath MSBuild variable to Common.proj

  • Adds Clean.bat for cleaning all binaries

  • Updates package_slvx.bat so Silverlight builds work out of the Git

  • Updates Alias.txt for Silverlight builds

Awesome work, Jimmy :slight_smile: