Move rigboard templates up a level

Also:
- Find and replace panel -> card
- Some base template work
- gulpfile things, added dep on django-gulp

RIGS/templates/invoice_list_active.html

@@ -0,0 +1,13 @@
+{% extends 'RIGS/invoice_list.html' %}
+
+{% block title %}
+Outstanding Invoices
+{% endblock %}
+
+{% block heading %}
+Outstanding Invoices ({{ count }} Events, £ {{ total|floatformat:2 }})
+{% endblock %}
+
+{% block description %}
+<p>Paperwork for these events has been sent to treasury, but the full balance has not yet appeared on a ledger</p>
+{% endblock %}