New Feature: Security PIN to lock channel

Added a new feature of Security PIN. The PIN allows completely locking the Rarflix channel from use.  I use this to separate parent tv-shows/movies from kids movies by using the Rarflix channel for parents and the simpler regular Plex channel for the kids with different myplex accounts.

The Security PIN is a sequence of pressing the directional arrows on the remote.  No nasty keyboard.

This is (hopefully) a precursor to full multiple user support.

It's meant to be merged against the test channel but it sounds like I didn't do it right.  Sorry about that - hope it's still useful.