Making taxon form to render attachment definitions dynamically

Solidus now allows to inject easily more attachment definitions via
configurable modules, if a user adds a new attachment, it would have
to override the partial _form to add this new attachment, this change
takes all definitions and render the inputs dinalycally, it also allows
to specify what partial to render depending on the attachment adapter.

backend/app/views/spree/admin/taxons/_form.html.erb

@@ -20,11 +20,7 @@
       </div>
     <% end %>
 
-    <%= f.field_container :icon do %>
-      <%= f.label :icon %><br />
-      <%= f.file_field :icon %>
-      <%= image_tag f.object.icon(:mini) if f.object.icon_present? %>
-    <% end %>
+    <%= render "spree/admin/taxons/attachment_forms/#{f.object.attachment_partial_name}", f: f %>
   </div>
 
   <div class="col-5">

backend/app/views/spree/admin/taxons/attachment_forms/_paperclip.html.erb

@@ -0,0 +1,7 @@
+<% f.object.class.attachment_definitions.each do |attachment, definition| %>
+  <%= f.field_container attachment do %>
+    <%= f.label attachment %><br>
+    <%= f.file_field attachment %>
+    <%= image_tag f.object.send(attachment, definition[:default_style]) if f.object.send(attachment).present? %>
+  <% end %>
+<% end %>

core/app/models/spree/taxon/paperclip_attachment.rb

@@ -18,4 +18,8 @@ module Spree::Taxon::PaperclipAttachment
   def icon_present?
     icon.present?
   end
+
+  def attachment_partial_name
+    'paperclip'
+  end
 end