objects

This pull request does two main things:

  * separate the various galaxy apis into separate sub-clients, much like the original bioblend API
  * add instance methods to the various wrappers

Four unit tests in TestGalaxyObjects still fail at this point:

  * test_dataset_get_stream (__main__.TestLibraryObject)
  * test_dataset_peek (__main__.TestLibraryObject)
  * test_dataset_download (__main__.TestLibraryObject)
  * test_dataset_get_contents (__main__.TestLibraryObject)