Filtering Tasks by their code name

Hey, 

I used nosetests to create a couple of tests. The actual login seemed tedious, so I monkeypatched my way around it, using canned data to test the feature. Except for the ``iron_core.IronClient.get`` requests everything is the real deal. 

I included a keyword argument to the ``IronWorker.tasks`` method. It defaults to an empty string. If it is set, its value is attached to the actual api request by using the code_name query string param. If the scheduled flag is set, the value will not be attached to the actual http request (because /schedules does not support the querystring parameter) but instead filters the list of tasks on the client after they were retrieved. 

I have been coding on my own for a long time now, so I would appreciate comments on everything, style, frameworks, and especially the monkeypatching. I believe the tests should run locally without people having to do actual http requests (I tried running them on the train without an internet connection...), therefore I faked out the iron_core.IronClient. 

To run the tests please do
```$ pip install -r requirements.txt```

```$ nosetests --verbose --tests test/test_iron_worker.py```

Regards from Germany