New System Status REST API

[dfaller]

Create an initial cut of a new v5 system status REST API. The API will return information contained in the scheduler's in-memory state related to nodes. The information will be synced to the Scale web server(s) from the scheduler on a regular basis from a background thread and should return a client response very quickly.

Later job failure/completion, load, and other information will be included. This API will become the new basis for the overview, node, and load pages in the Scale UI.