don't hard code the shoppingcart order confirmation page to use settings.xxx, allow for microsites to override

lms/templates/shoppingcart/receipt.html

@@ -1,6 +1,7 @@
 <%! from django.utils.translation import ugettext as _ %>
 <%! from django.core.urlresolvers import reverse %>
 <%! from django.conf import settings %>
+<%! from microsite_configuration import microsite %>
 
 <%inherit file="../main.html" />
 
@@ -22,7 +23,7 @@
   <section class="wrapper cart-list">
     <div class="wrapper-content-main">
       <article class="content-main">
-        <h1>${_(settings.PLATFORM_NAME + " (" + settings.SITE_NAME + ")" + " Electronic Receipt")}</h1>
+        <h1>${_("{platform_name} ({site_name}) Electronic Receipt").format(platform_name=microsite.get_value('platform_name', settings.PLATFORM_NAME), site_name=microsite.get_value('SITE_NAME', settings.SITE_NAME))}</h1>
         <hr />
 
         <table class="order-receipt">