Add GWR advance ticket availability date

Closes: #33

templates/index.html

@@ -24,6 +24,7 @@
   "xmas_day": "Christmas day",
   "next_up_series": "Next Up documentary",
   "waste_schedule": "Waste schedule",
+  "gwr_advance_tickets": "GWR advance tickets",
 }
 %}
 
@@ -46,6 +47,13 @@
     <ul>
     <li>Today is {{now.strftime("%A, %-d %b %Y")}}</li>
     <li>GBPUSD: {{"{:,.3f}".format(gbpusd)}}</li>
+    <li>GWR advance ticket furthest date:
+      {% if gwr_advance_tickets %}
+        {{ gwr_advance_tickets.strftime("%A, %-d %b %Y") }}
+      {% else %}
+        unknown
+      {% endif %}
+    </li>
     </ul>
 
   <table class="table table-hover w-auto">