LAVA-441 - drop render_to_response({}, RequestContext(request)
Switch to loader.get_template(), HttpResponse(template.render({}, request))
render_to_response with a RequestContext has been removed from
django1.10 and raises an exception related to the context_processor.
Drop use of SumIf and replace with conditional expressions.
Handle tightening of filters on isnull conditions when blank
is allowed for the foreignkey. (Prevents jobs starting with 1.10)

Change-Id: I59cf9caa0fe3a82027dec0caad5993cda158791b