When importing a dataset into a history, update the history's list of dataset ids
Add History object unit tests
Fix inexistant argument in call to delete
Update library dataset_id list when uploading
Unit tests for library wrapper object
Use NamedTemporaryFile instead of manually deleting
Correct errors with object interface

This commit got out of hand regarding its size. Most changes are
related to the work on the object-oriented interface. Other than
correcting bugs and adding unit tests, this commit contains:

  * remove the datasets API
  * changed History and Library clients to derive the Dataset client
  * new call to refresh the contents of an object
  * new call to wait for a history dataset to reach a definitive state