Adds the basic things needed for procedures:
- add message and endpoint types:
- rename MessageOp.SET to MessageOp.KEY_VALUE
- add MessageOp entries for set operations
- add functions in redis_connector:
- to interact with clients
- to interact with sets
- add procedure infra:
- manager distributes request queue to workers
- worker base class which times out when its
queue is empty for too long
- simple runner for testing