Implement stream action as defined in EDV

[talwinder50]

The Stream section would be lower priority.

https://digitalbazaar.github.io/encrypted-data-vaults/#data-vault-https-api

[dlongley]

Also -- the stream portion of the spec is quite out of date/out of sync with implementations. Please take a look at https://github.com/digitalbazaar/edv-client when comparing your implementation. We expect to be updating the spec to better match implementations -- as implementations provided a lot of experience that should now feed back into improving the spec.