Added Queue problem and empty setup/solution.

A levelmeup queue datatype problem for levelmeup.

The main focus is showing how easy it is to develop new datatypes on top of LevelUp.

However, I'm finding some problems in writing the setup.js to allow to require a module and execute it.
I've looked at the "horse_js_tweets" exercise, and I don't know exactly how to refactor the code to generalize the "writing modules tutorials". Maybe this feature might go into workshopper itself.