Import library datasets in history, so they get numbered.
Add 'deleted' to HistoryDatasetAssociation BASE_ATTRS.
Merge pull request #7 from nsoranzo/objects

Small enhancements
Merge remote-tracking branch 'origin/objects' into objects
added first stub of ToolClient
added docs to upload_from_galaxy_fs
extended and unified get_preview docs
added object deletion by name
changed object-level delete to pass id to gi-level delete as a kwarg