Parallelize queue parsing in API

[campb303]

Currently, when the /api/data/<queue> is processed, queues are parses sequentially:

queue_list = []
for queue in queues_requested:
    queue_list.append(_Queue(queue, headers_only=headers_only).to_json())
return (queue_list, 200)

Rewriting this to support threading i.e. loading multiple queues simultaneously could result in significant performance increases by a factor of the number of concurrent processes possible.

[campb303]

Fixed in #45