Panoptes-client

- Fix: Bearer token checking only occurs when necessary

- New: Support for all data exports
- New: Project owners can update `ProjectPreference` settings
- New: Removed `subject_sets` method and `SetMemberSubject` (now in links)
- New: Add set to iterable types
- Fix: Only save links if it's been modified
- Fix: Specify minimum requests version

- New: Add User model
- New: Add option for env vars for auth
- New: Add scope kwarg to Classification.where()
- New: Add SetMemberSubject class
- New: Submit subject links in batches in SubjectSet.add()
- New: oauth for client apps
- Fix: Skip trying to read export state if description was empty
- Fix: Don't rely on the response having a Content-Length header

- New: Automatically retry failed image uploads
- New: Project classifications export
- New: Subject retirement in Workflow
- New: Add client ID for panoptes-staging.zooniverse.org
- New: Add ProjectPreferences
- New: Add Classification
- New: Removing subject set links
- Fix: IOError: Too many open files (in subject.py, line 64) 6

- Initial release!
- Allows creating and modifying projects, subjects, subject sets