added webservice methods to retrieve performance data

Not ready for merge yet. Just creating for review.
There's no need to use json here. ``request.QUERY_PARAMS`` is a more correctly named synonym for django's ``request.GET`` which is an instance of ``django.http.QueryDict`` which has a full dictionary interface.  Try replacing the ``request.QUERY_PARAMS.get()`` with ``request.QUERY_PARAMS.dict()`` and remove the ``properties`` parameter from the uri structure and the call to ``json.loads``. 

https://docs.djangoproject.com/en/dev/ref/request-response/#django.http.HttpRequest.GET
https://docs.djangoproject.com/en/dev/ref/request-response/#querydict-objects