Adding explicit require for sipity/jobs

For some reason specs fail when I use the following command

```console
$ rspec --pattern ./spec/jobs/\*\*/\*_spec.rb
```
Adding spec for DoiCreationRequest defaults
Adding spec and reasoning for Sipity::Models
Moving Policy questions to Sipity::Policies
Extracting method to more appropriate location

The authorization layer is responsible for negotiating between the
context (controller) and the policy layer; As such I want to tease
apart that boundary and make it more decoupled.
Tidying up an incorrect spec
Adding and removing commentary

[skip ci]
Reworking method signature

To bring things more in line with the DoiMethods' various method
signatures, I'm replacing the use of header_id with header.
Adding a REVIEW concerning REDIS & job parameters

[skip ci]
Switching DoiCreationRequestJob to use header_id

Given that there is a database constraint on the DoiCreationRequest,
the repository/job interaction is easier to handle if I am passing the
header_id instead of the doi_creation_request_id.

I am also able to remove some object persistence.
Merge pull request #25 from ndlib/switching-doi-creation-request-to-header-id

Switching DoiCreationRequestJob to use header_id