Basic infrastructure for publishing a REST API.

Copied unmodified from HybridCluster repository, except that:
1. Paging logic was ripped out.
2. Updated to latest Eliot APIs.
Make package externally usable.
Minimal example usage of the API package.
Lint fixes.
Update some dependencies.
Split testing infrastructure into private and public parts.
Delete some unused code.
Remove hybridcluster references.
Add RPM dependencies.
Rename module.
Address review comments: Copyright headers.
Address review comment: Link to Eliot issue.
Address review comment: Make more APIs public.
Address review comment: Document schema_store.
Fix import.
Merge pull request #894 from ClusterHQ/http-api-886

HTTP REST API infrastructure.

Fixes #886.