FEAT: Add periodic cleanup command

Currently performs two functions:
1. Inactivates users that have not logged in for at least one year. Closes #478 (Need to circle back round to full deletion SoonTM)
2. Ensures the supervisor database flag is set correctly for each user

This is run automatically by the Heroku Scheduler addon at midnight daily.

templates/form_errors.html

@@ -1,13 +1,12 @@
 {% load nice_errors from filters %}
 {% if form.errors %}
-	<div class="alert alert-danger alert-dismissable">
-		<button type="button" class="close" data-dismiss="alert" aria-hidden="true">&times;</button>
+	<div class="alert alert-danger mb-0">
 		<dl>
 			{% with form|nice_errors as qq %}
 				{% for error_name,desc in qq.items %}
                 <span class="row">
-				    <dt class="col-4">{{error_name}}</dt>
-				    <dd class="col-8">{{desc}}</dd>
+				    <dt class="col-3">{{error_name}}</dt>
+				    <dd class="col-9">{{desc}}</dd>
                 </span>
 				{% endfor %}
 			{% endwith %}

templates/registration/loginform.html

@@ -1,5 +1,10 @@
 {% load widget_tweaks %}
 {% include 'form_errors.html' %}
+{% if form.errors %}
+	<div class="alert alert-info">
+		<p><strong>Please note:</strong> If it has been more than a year since you last logged in, your account will have been automatically deactivated. Contact <a href="mailto:it@nottinghamtec.co.uk">it@nottinghamtec.co.uk</a> for assistance.</p>
+	</div>
+{% endif %}
 <div class="col-sm-6 offset-sm-3 col-lg-4 offset-lg-4">
     <form action="{% url 'login' %}" method="post" role="form" target="_self">{% csrf_token %}
         <div class="form-group">