Create API endpoint to persist Workspace

[machristie]

Need a CRUD REST API endpoint for the Workspace data structure.

TODO

• [x] create scenarios
• [x] create sources and sinks associated with scenario
• [x] create the experiments associated with scenario
• [x] add/update scenarios
• [x] add/update sources and sinks associated with scenario
• [x] add/update experiments associated with scenario
• [x] add derived fields to experiment serializer (experiment name, url, state, result)
• [x] integrate with UI - save_workspace
• [x] -handle source and sink fields - maybe derive them from the geojson file?- for now ids are sufficient
• [x] validate unique workspace name and unique scenario title
• [x] (maybe separate issue) when creating experiment for a workspace, it should be created in the Airavata project that belongs to the Case's SimCCS Project
• [x] add created/updated date to workspace