Merge branch '19171-pinned-width' into 'master'

Resolve "Pin should show up at 1280px min"

Decreased window min width for pinned sidebar

Closes  #19171
Part of #19200

![Screen_Shot_2016-06-27_at_9.36.13_AM](/uploads/d0a87bca5af1bee808c5b1046c0ecf72/Screen_Shot_2016-06-27_at_9.36.13_AM.png)

See merge request !4947
(cherry picked from commit bbbd0e6c)

app/assets/javascripts/application.js.coffee

@@ -255,7 +255,7 @@ $ ->
   new Aside()
 
   # Sidenav pinning
-  if $(window).width() < 1440 and $.cookie('pin_nav') is 'true'
+  if $window.width() < 1280 and $.cookie('pin_nav') is 'true'
     $.cookie('pin_nav', 'false', { path: '/' })
     $('.page-with-sidebar')
       .toggleClass('page-sidebar-collapsed page-sidebar-expanded')

app/assets/stylesheets/framework/variables.scss

@@ -7,7 +7,7 @@ $gutter_collapsed_width: 62px;
 $gutter_width: 290px;
 $gutter_inner_width: 258px;
 $sidebar-transition-duration: .15s;
-$sidebar-breakpoint: 1440px;
+$sidebar-breakpoint: 1280px;
 
 /*
  * UI elements