Ahodges/documentation/doc608

@gwprice , @jimabramson , @marcotuts , @lou-wang , @explorerleslie , @WatsonEmily  please check accuracy and completeness (note the files have different audiences, staff vs. students).
@mhoeber @srpearce please copy edit.
@mslotkeEDX , I agree that this is a pretty clunky way to refer to the selection control on the Discussion page. It doesn't have an explicit label in the UI (and I don't think it needs one), so I am left to my own devices to come up with something short & descriptive. Your thoughts welcome! I did go through both chapters, and made sure that I am explicitly giving the location of this list "on the **Discussion** page" rather than making an assumption that they will instantly know what this is. Let me know what you think.