Messaging: throw on empty argument to constructors

* Check for emptyness upon initialization of QueueServiceSender
  and PublisherService. If any constructor argument is empty,
  then throw an IllegalArgumentException and state what's empty.
  The effect of this is that the caller will know upon construction
  that something is wrong, instead of noticing when trying to
  publish the message.
* Cleanup javadoc after comments; do not indend parameter descriptions.