Make PanelsIPEPageController more extensible

Problem/Motivation

Overriding the PanelsIPEPageController routes is difficult, because the method return the instantiated JsonResponse.

Proposed resolution

Break the current route methods into two methods, the first returns an array, and the second returns the JsonResponse. With this delineation, an overriding class could override the data method, alter the data, and then let it be returns by the Json method.

Remaining tasks

review code and merge

User interface changes

none

API changes

Existing API's don't change but new methods are created.

Data model changes

none