prep for mobile

* index route simplified
  * no longer a need to store all pantries at bottom of page
* #content div is gone; less elements == more happy
* rename of key div's:
  * #mainHeader -> #header
  * #leftContainer broken up; won't really be 'left' for mobile
    * #search followed by #pantryList
* #searchIndicatorBar is gone
  * messages not super helpful + space is important for mobile
  * search() function replaced by underlying Backbone fn
* #social moved towards the bottom, which will help page load perf
* minor CSS tweaks
make "fork me on GitHub" for desktop only

A simple media query that only hides the image for small screens
combine PantryListingsView into PantriesView
make all of main.js strict
re-org: Backbone, then Helpers, OnLoad
consolidate styles: var foo = function() {}..
optimize PantriesView.render

This is admittedly a small win, but it's easy. Stop checking into other
branches if we've got what we came to do.
on PantriesView.render, scroll list to top
rename findRadius arg from bounds to mapBounds

it's at least a bit more descriptive
searchAgain renamed to searchByMap
mobile-friendly, responsive design

First implementation of
https://github.com/codeforboston/pantry_pickup/issues/6