[Delete] serve delete API

[zelima]

We are implementing purge commend so we need an API for it. As specstore has access for all involved instances this makes it the best place to serve.

Acceptance Criteria

• User is authorized and Authenticated before deleting anything
• After request there is no data either in pkgstrore, metastore, or specstore

Tasks

• Authorization
  • Prepare tests
  • Add function that returns True if authorised
• Delete from metastore (Elasticsearch)
  • Prepare Tests
  • add apropriate method to datasets https://github.com/datahq/specstore/blob/master/flowmanager/datasets.py
• Delete from pkgstore (S3)
  • Prepare tests
  • appropriate function in models
• Delete from specstre (database)
  • Prepare tests
  • delete fromdatasets
  • delete from revisions
• serve endpoint