Feature/156 simple content workflow

[jmurty]

Create a new workflow application in ICEKit where we will add very basic workflow-like content management features such as:

• assign a user to a specific content item
• set basic workflow status information, such as "new" or "in review"
• provide information about who created or edited items

We anticipate doing most of the work using a combination of Django's Generic Foreign Keys (GFKs) so we can relate workflow information to any model, and admin mixins to expose the workflow fields for staff to edit.

[coveralls]

Coverage decreased (-0.05%) to 73.396% when pulling 23d2a208686c27d0e3c9aba6688f265dae92ffe6 on feature/156-simple-content-workflow into 307b792e1d472ec0df44bad13066ac020f91a186 on develop.

[coveralls]

Coverage decreased (-0.4%) to 73.055% when pulling f7556a150de48ad57cdaec890201de5f4bb7f617 on feature/156-simple-content-workflow into 307b792e1d472ec0df44bad13066ac020f91a186 on develop.

[coveralls]

Coverage increased (+1.1%) to 74.227% when pulling 4ffb3c1c30814f5e74e2e88caa5f6a615677f913 on feature/156-simple-content-workflow into f9fff6a050e8c064b642dcaf4623b08c54909619 on develop.

[coveralls]

Coverage increased (+1.1%) to 74.252% when pulling 2a6caaebf6b23f6ecf8b56cc4bf93fd3c801a23e on feature/156-simple-content-workflow into f9fff6a050e8c064b642dcaf4623b08c54909619 on develop.