Invoices: provide overridable template blocks

pootle/templates/invoices/invoice.html

@@ -129,7 +129,7 @@
     <div class="border">
       <table class="header">
         <tr>
-          <td rowspan="4" class="logo"></td>
+          <td rowspan="4" class="logo">{% block logo %}{% endblock %}</td>
           <td class="label">INVOICE:</td>
           <td class="value">{{ id }}</td>
         </tr>

pootle/templates/invoices/invoice_message.html

@@ -14,6 +14,7 @@
       </p>
     {% endif %}
 
+    {% block body %}
     {% if accounting %}
       <p>This email is sent automatically by {{ POOTLE_TITLE }} on behalf of the user.</p>
 
@@ -23,6 +24,7 @@
 
       <p>In case of questions, please contact our your managers at [email protected]</p>
     {% endif %}
+    {% endblock %}
 
     {% include 'invoices/_email_invoice_table.html' %}
   </body>

pootle/templates/invoices/no_invoice_message.html

@@ -14,6 +14,7 @@
       </p>
     {% endif %}
 
+    {% block body %}
     {% if correction_added %}
       <p>This is to inform you that your balance at {{ POOTLE_TITLE }} is {{ balance }} {{ user.currency }}, which is less than the minimal payment of {{ minimal_payment }} {{ user.currency }} defined for your account.</p>
       <p>Because of this, there will be no payments from us during this payment cycle. The amount of {{ balance }} {{ user.currency }} will be carried over to the next payment cycle. You will see two corrections in your statistics dashboard reflecting the carry-over (one in the previous month, and on in the current one).</p>
@@ -26,5 +27,6 @@
     <p>
       In case of questions, please contact our managers at [email protected]
     </p>
+    {% endblock %}
   </body>
 </html>