Navigation changes

New navigation is ready to look at! My biggest concern is whether or not things will still work with all of the work everyone else has been doing because in order to implement the navigation bar, I changed how files extend to each other. For some, I've extended html files across folders that are not really related to each other; for example, I've extended "update_videos.html" from "base.html" in the "control_panel" folder instead of the "updates" folder, and similarly with "update_languages." Please take a look at the extensions on each of the html files I've changed if you can.

If you're confused as to why there are two of the same navigation bars coded in on each of the pages, it's because each will be visible according to what kind of user is logged in, admin or teacher, toggled by the css class "teacher-only" and "not-teacher-only" and has the appropriate tabs for each user.

Also, I found that Effort versus Achievement and Mastery over Time do not display under coach reports when you try to view data, but I don't know if it's because of the changes I made or because my computer just has issues with the current branch (I can't get student playlists to show on my computer either).

And please disregard the changes I made to "zone_management.html" in regard to the section that links to "device_management.html" and which are not related to the navigation bar. I hacked around a little bit to be able to access the device page because for some reason I couldn't do it from my end and I don't think the device data displays correctly right now. 

Other concerns: What are your thoughts on the CSS being sort of hardcoded into style tags on the base.html pages in the control_panel and coachreports folders instead of in their own CSS files? 
Might be good to make these class names a bit more specific, to avoid conflicts with other elements that might exist or be added later. E.g. `.subnav-users`