Allow saving a draft without editorial workflow

**- Do you want to request a *feature* or report a *bug*?**

Feature

**- What is the current behavior?**

Draft saving (eg. not publishing, but allowing saving to the repo in some way) of an item/post without having the entire Editorial Workflow enabled.

**- What is the expected behavior?**

Allow saving as a Draft, as shown in the UI mockups for 1.0

**Change of terms:**

"Draft" is now universal term for the antonym of published
"Working" is now the term for the first state of editorial workflow
"Save" button in editor should be "Save draft"

Additional:
Unpublishing, if made possible, would revert a published item/post to a draft. https://github.com/netlify/netlify-cms/issues/727https://github.com/netlify/netlify-cms/issues/727

Tangentially related to this as well: https://github.com/netlify/netlify-cms/issues/388