FEATURE: Add CustomUserResourceIndex for wrapping custom secondary indexs to lookup resources based on current page.
UIResults provides access to custom resource index via getCustomResourceIndex() and
getCustomResourcePaths() which find the index object in the access point userProps.

CustomUserResourceIndex.getCustomResourcesPathsAsJSON() is a utility function which also looks up and extracts
a field from the index for the current requestUrl and returns a JSON string of the matching results

UIResults.getCustomResourcePaths() combines getCustomResourceIndex() and getCustomResourcesPathAsJSON() calls
for convenience