Clean up front-end code for develop all the things branch 

Opening this PR now as a way to track the to-do list progress. I've just gone through and made a list of issues, copied below. I'll track progress internally in my dev journal and report back on significant process. I'm going to focus on what I think is higher priority stuff like fixing wacky subnav and making the code more readable, and then if time, adding bootstrap styles to stuff. 

All users: 
* Use bootstrap 3 grid system globally... 
* Push footer to bottom
* update login button to use bootstrap button styles 
* Showing error message when clicking “Sign Up” as a logged out user and redirecting to login => You must be logged in with an account authorized to view this page.
* help page needs help
* footer links should go places if online
    * CC, FLE, Khan Academy
* Refactor messages, nav into partials
* At half-width
    * KA Lite logo is unnecessarily small 
* At phone width
    *footer bunching on the left rather than stacking  nicely

Logged in as super admin:
* Manage => Zone management page
    *subnav icons are wacky
    * Facility and device tables are wacky
    * This template is massive => partials 
    * Put downloaded languages into a table
    * Videos
       * Update buttons to use bootstrap styling (same for language page) 
       * Update “boxes” to use bootstrap styling (same for language page) 
    * At half width
       * Tables off the screen 
       * Logged in name overlaps with navigation 
    * Teach => 
        * subnav needs a bit of tweaking to get hover effect right and link should span entire tab 
        * Playlist page is rendering and then overriding something so it flashes 
        * Current Units page needs to inherit from the right base templates to inherit the styles 
        * If admin clicks “Learn” they lose their subnav
    * At phone width
         * Playlist assignment needs bootrap grid, currently off the page 
         * Exams are halfway there, but need to be inside a container 
         * Units page buttons are stacking strangely 

Logged in as teacher:
  * Teach ==> 
    * not seeing test report coach report option 
    * coach reports should really just default to one view and show options to navigate to others 
  * At half width
    * Coach reports stacking strangely (think about another way to show the options 
  * At phone width
    * Subnav needs to shrink, it pushes itself off the screen

  * Manage ==> 
    * subnav needs tweaking 
    * users & facilities page needs to be consolidated - they can’t be sibling nav items because they are     hierarchical in nature 

Logged in as student
  * when assigned playlists is empty, hide the bar 
  * playlist progress reports are broken