Add app estimator lookup function

[briehl]

similar to other app lookup functions in catalog, can be run with:

catalog.get_app_resource_estimator({
    "module_name": "SomeModule",
    "app_id": "some_method",
    "tag": "release"
})

or

catalog.get_app_resource_estimator({
    "app_id": "some_nms_only_module"  # or "SomeModule.some_method"
})

returns

{
    "estimator_module": "SomeModule",
    "estimator_method": "an_estimator_method"
    "tag": "release"  # (or "beta" or "dev")
}

If an estimator isn't found, those values are null.

To get this to work right, I changed two things for testing.

1. Changed the NMS submodule to the develop branch (that's only used for testing anyway)
2. Changed the narrative_method_specs it uses to the test branch, which it should probably be using anyway.

Other than that, it's pretty straightforward. Main changes are in catalog.spec, controller.py, and app_estimator_test.py

[briehl]

@scanon @bio-boris ^^