Extract functions in foundation extras

In foundation extras we were assigning functions to local variables, but
in the rest of the CoffeeScript files we use them as object properties.

app/assets/javascripts/foundation_extras.js.coffee

@@ -1,24 +1,21 @@
 App.FoundationExtras =
+  clearSticky: ->
+    $("[data-sticky]").foundation("destroy") if $("[data-sticky]").length
+
+  mobile_ui_init: ->
+    $(window).trigger "load.zf.sticky"
+
+  desktop_ui_init: ->
+    $(window).trigger "init.zf.sticky"
 
   initialize: ->
     $(document).foundation()
     $(window).trigger "resize"
-
+    $(document).on("page:before-unload", this.clearSticky)
-    clearSticky = ->
+    window.addEventListener("popstate", this.clearSticky, false)
-      $("[data-sticky]").foundation("destroy") if $("[data-sticky]").length
-
-    $(document).on("page:before-unload", clearSticky)
-
-    window.addEventListener("popstate", clearSticky, false)
-
-    mobile_ui_init = ->
-      $(window).trigger "load.zf.sticky"
-
-    desktop_ui_init = ->
-      $(window).trigger "init.zf.sticky"
 
     $ ->
       if $(window).width() < 620
-        do mobile_ui_init
+        App.FoundationExtras.mobile_ui_init()
       else
-        do desktop_ui_init
+        App.FoundationExtras.desktop_ui_init()