Allow Tasks query to leave the queue specification blank if ID is specified

[shiblon]

If we know a task's ID and just want to get it, we don't need the queue. We should be able to query for tasks based on more than one queue, based on ID, etc., but not always require a queue specification.

[shiblon]

This would allow the command line client eqc "mod" command to not need to send the queue to the "tasks" query, which would allow that particular flag to be omitted on the commandline.

Quite often you just want to delete a task by ID, and this would make that simpler for users.