Move templates in app directory

corres2math/templates/500.html

@@ -0,0 +1,8 @@
+{% extends "base.html" %}
+
+{% load i18n %}
+
+{% block content %}
+    <h1>{% trans "Server error" %}</h1>
+    {% blocktrans %}Sorry, an error occurred when processing your request. An email has been sent to webmasters with the detail of the error, and this will be fixed soon. You can now watch some videos.{% endblocktrans %}
+{% endblock %}