Add three methods for pulling only children objects that the currently authenticated user can read.  Move some shared code into the less confusing SetsHelper, instead of just using it from NuCollectionsHelper.  Include SetsHelper for the collection and community controllers.
Move current_user_can read/edit? methods out of application_helper and into application_controller, where they belong.
Refactor helper methods for filtering children objects into set controllers, make collection/community controllers subclasses off that.
Merge branch 'develop' into feature/set_helpers

Conflicts:
	app/controllers/communities_controller.rb

Accidentally made a few commits directly onto develop.
Fixing up some changes lost in the merge.
remove reference to sets_helper in nu collection controller.
Merge pull request #124 from nu-lts/feature/set_helpers

Feature/set helpers