Add "min % diff" option for pricing batch from products query

refactor the "batch from query" a bit also, to allow for multiple batch type
options which represent the same underlying batch type.  (thought i needed
that, then realized i didn't, but seems safe to include.)

tailbone/templates/products/batch.mako

@@ -1,7 +1,7 @@
 ## -*- coding: utf-8; -*-
 <%inherit file="/base.mako" />
 
-<%def name="title()">Products: Create Batch</%def>
+<%def name="title()">Create Batch</%def>
 
 <%def name="context_menu_items()">
   <li>${h.link_to("Back to Products", url('products'))}</li>