Add rake task to create all topics on govdelivery

We need to provide the ability for users to sign up for a format, with
filters based on a single field.

This rake task precreates all the necessary topics for each combination
of options. For formats with no options, it will create a single list
for the entire format.
Push signup options to publishing api

finder front end will use these to build the checkbox options for a
format.
Merge pull request #80 from alphagov/email_topic_creation

Create topics on govdelivery for each format