Refactor the build scripts

- Bifurcate Package and Publish targets to enable signing.
- Move publish from bash/ps into c#.
- Create multiple targets to create MSIs and Bundles.

scripts/Microsoft.DotNet.Cli.Build.Framework/Enumerations/BuildPlatform.cs

@@ -3,8 +3,10 @@ namespace Microsoft.DotNet.Cli.Build.Framework
     public enum BuildPlatform
     {
         Windows = 1,
-        OSX = 2,
-        Ubuntu = 3,
-        CentOS = 4
+        Unix = 2,
+        Linux = 3,
+        OSX = 4,
+        Ubuntu = 5,
+        CentOS = 6
     }
-}
+}