For #194, convert the POTD management command to a celery task. Refactored to put the logic for the command into a function, and the command simply calls this function. The task can also just call this function. Added some basic tests for the new function.

{% extends 'base.html' %}
{% block title %}{{ flatpage.title }}{% endblock %}
{% block content %}
<h2>{{ flatpage.title }}</h2>
{{ flatpage.content }}
{% endblock %}