Simplify new image "inline" form

There's no need to do ajax here, we can render the form when we load the
page.

backend/app/assets/javascripts/spree/backend/images/index.js

@@ -2,16 +2,7 @@ Spree.ready(function() {
   $('#new_image_link').click(function(event) {
     event.preventDefault();
 
-    $('.no-objects-found').hide();
-
     $(this).hide();
-    Spree.ajax({
-      type: 'GET',
-      url: this.href,
-      success: function(r) {
-        $('#images').html(r);
-        $('select.select2').select2();
-      }
-    });
+    $('#new_image').show();
   });
 });

backend/app/views/spree/admin/images/_new.html.erb

@@ -0,0 +1,12 @@
+<%= form_for [:admin, product, image], html: { multipart: true } do |f| %>
+  <fieldset data-hook="new_image">
+    <legend align="center"><%= t('spree.new_image') %></legend>
+
+      <%= render partial: 'form', locals: { f: f } %>
+
+      <div class="form-buttons filter-actions actions" data-hook="buttons">
+        <%= button t('spree.actions.update') %>
+        <%= link_to t('spree.actions.cancel'), admin_product_images_url(@product), id: 'cancel_link', class: 'button' %>
+      </div>
+  </fieldset>
+<% end %>

backend/app/views/spree/admin/images/index.html.erb

@@ -9,7 +9,9 @@
   <% end %>
 <% end %>
 
-<div id="images" data-hook></div>
+<div id="new_image" class="hidden">
+  <%= render 'new', product: @product, image: Spree::Image.new(viewable: @product) %>
+</div>
 
 <fieldset>
   <legend align="center"><%= t(".upload_images") %></legend>

backend/app/views/spree/admin/images/new.html.erb

@@ -1,12 +1 @@
-<%= form_for [:admin, @product, @image], html: { multipart: true } do |f| %>
-  <fieldset data-hook="new_image">
-    <legend align="center"><%= t('spree.new_image') %></legend>
-
-      <%= render partial: 'form', locals: { f: f } %>
-
-      <div class="form-buttons filter-actions actions" data-hook="buttons">
-        <%= button t('spree.actions.update') %>
-        <%= link_to t('spree.actions.cancel'), admin_product_images_url(@product), id: 'cancel_link', class: 'button' %>
-      </div>
-  </fieldset>
-<% end %>
+<%= render 'new', product: @product, image: @image %>