Improve JSON v1 operator API performance.

According to some user reports, a simple comparison of the v1 operator API (using the "GET_TASKS" call) and the v0 /tasks HTTP endpoint shows that the v1 API suffers from an inefficient implementation:

Operator HTTP API (GET_TASKS): 0.02s user 0.08s system 1% cpu 9.883 total
Old /tasks API: /tasks: 0.00s user 0.00s system 1% cpu 0.222 total

Looking over the implementation, it suffers from the same issues we originally had with the JSON endpoints:

• Excessive copying up the "tree" of state building calls.
• Building up the state object as opposed to directly serializing it.