Fixes Bugs with the CLI Messaging module

* Adds messaging service to the main help so it can be discovered
* Fixes an issue that occurred if the user didn't have permission to manage
  message queue accounts.
* Changes SoftLayer.exceptions.Unauthenticated to be a SoftLayerError instead of StandardError
Merge pull request #210 from sudorandom/master

Fixes Bugs with the CLI Messaging module