Add support for FB Page Insights Endpoints

[theclue]

DIFFICULT: this is going to be a pain in the neck

Currently, facebook.S4 only support public-face endpoints (for ex. posts, comments, conversations, private message, walls, feed, photos, etc.)

But the most valuable data to put to perform analysis are the Facebook Page Insights, providing metrics about the page the logged users admins.

facebook.S4 should add support for FB Insights data as well enanching the ### FacebookPagesCollection S4 class or ### providing a new collection type (suggestions well appreciated!)

This is going to be hard, as FB Insights structs are huge in both rows and columns.

HACKTOBERFEST: pull requests against this issue are elegible to rewards in the contexct of the Hactoberfest 2018