v6 Scheduler REST API

[dfaller]

Create new v6 scheduler REST APIs. Add docs to new v6 section of the REST API docs.

New addition for v6: Add a new char field to the scheduler model called resource_level with valid values of "TOO HIGH", "TOO LOW", and "GOOD". The new field should have a default value of "GOOD".

Add the new field to the response in the GET scheduler API and make the field editable by the PATCH scheduler API. Also make the PATCH scheduler API simply return a 204 No Content without any response body.