For #242, move the updating of the POTD sequence into a new signals module. When photos are deleted from the admin changelist in bulk, the individual delete() functions on the photo objects is not called. However, the post_delete signal is called for each object.

"""
Celery tasks for the POTD app.

"""
from celery.task import task

import potd.tools


@task
def pick_potd():
    potd.tools.pick_potd()