Programmable Gateways

[sarahwooders]

Changes:

• Add Pipeline object for queueing multiple jobs (example in python examples/test_pipeline.py. )
• Require Dataplane creation to provide a topology plan
• Modify gateways to run on gateway programs
• Modify planner (planner.py) to generate a TopologPlan object which can be compiled into a gateway program JSON to be provided to gateways
• Modify ProgressBarTransferHook to support tracking multiple destinations
• Support pipelining upload ID generation for multipart transfers by adding a /api/v1/upload_id_maps endpoint to Gateway API to send upload ID mappings to gateways along with chunk dispatching

[sarahwooders]

I made an issue for adding gateway components tests #806, since ideally we can get this merged asap