Find first image using handlebars

When I first wrote this I didn't know how to index an array in
handlebars. Now I do!

This is better to have in handlebars because it's simpler and the JS
doesn't need to care that an image is being displayed.

backend/app/assets/javascripts/spree/backend/templates/orders/line_item.hbs

@@ -4,7 +4,7 @@
   </td>
 {{else}}
   <td class="line-item-image">
-    {{> _image image=image size="mini" }}
+    {{> _image image=line_item.variant.images.[0] size="mini" }}
   </td>
   <td class="line-item-name">
     {{ line_item.variant.name }}<br>

backend/app/assets/javascripts/spree/backend/templates/variants/autocomplete.hbs

@@ -1,6 +1,6 @@
 <div class="variant-autocomplete-item media">
   <div class="media-left">
-    {{> _image image=image size="mini" }}
+    {{> _image image=variant.images.[0] size="mini" }}
   </div>
 
   <div class="media-body">

backend/app/assets/javascripts/spree/backend/variant_autocomplete.js.coffee

@@ -3,10 +3,8 @@
 variantTemplate = HandlebarsTemplates["variants/autocomplete"]
 
 formatVariantResult = (variant) ->
-  image = variant.images[0]
   variantTemplate(
     variant: variant
-    image: image
   )
 
 $.fn.variantAutocomplete = (searchOptions = {}) ->

backend/app/assets/javascripts/spree/backend/views/cart/line_item_row.js

@@ -76,11 +76,8 @@ Spree.Views.Cart.LineItemRow = Backbone.View.extend({
   },
 
   render: function() {
-    var line_item = this.model.attributes
-    var image = line_item.variant && line_item.variant.images[0]
     var html = HandlebarsTemplates['orders/line_item']({
-      line_item: line_item,
-      image: image,
+      line_item: this.model.toJSON(),
       editing: this.editing,
       isNew: this.model.isNew(),
       noCancel: this.model.isNew() && this.model.collection.length == 1