Create inserts a new instance object in DB, sets its heartbeat routine in motion.

ListInstances returns a list of µTask instances from DB.

HeartbeatInterval is the duration between an instance's heartbeats a heartbeat is a sign of life, committed to DB, for an instance to assert that it is still active useful to discriminate tasks acquired by a defunct instance.

Instance represents one active instance of µTask with its ID acquired from DB, and its latest heartbeat timestamp.