InnerServer loses stacktrace of exceptions, making it harder to debug issues

[NickAb]

Our sync invoke method rethrows captured exception with new stacktrace, losing crucial information that could be helpful while debugging. See CommandBase.cs#L96 for StoreApps. Same thing for Silverlight.

We should keep original stacktrace using something like throw new Exception(message, ex) and making sure that final json response includes message and stacktrace both of exception and any of its inner exceptions.