Adding tenant to stores and APIs. To do this, introducing the
concept of an Account to keep track of all user information, and
views for the cluster and entity stores. Views are per account,
and only allow access to parts of the database that can be
accessed by that account.
pull request feedback.  Moving node, job, task calls out of
the ClusterStoreService and putting it in a ClusterStore class
that is able to see the full store.
remove unused imports.
Merge pull request #245 from continuuity/feature/tenant-in-stores

Adding tenant to stores and APIs. To do this, introducing the