Give api server operation tracking ability

Pending and recently completed operations now served at: /api/v1beta1/operations/id#

Handling of async operations is now consistent and sensible (ish). We check for admissibility before starting a long wait. I added some ID != "" checks here, but probably more things should be checked.
Let's make this have a buffer of size 1 so that writes to the channel don't block on the read.