Task IDs.

- create task ids, each task gets an id when it is sent, id generated
with redis
- setID can be called only once, it should not be used by the clients of
tasks
- in TASK_HASH, we put (taskID, task)
- in the set of tasks only task ids are stored
- in the map of timestamps, key = task id and value is the time at which
the task was taken