Make redirects support different post statuses

[GaryJones]

As per #125 (comment) when redirect posts are added, they end up with a draft post status.

To enable a concept of active and inactive (and trashed #125) redirects, we need to:

• Insert new redirects with a publish post status.
• Have an update mechanism in a release to update existing redirects to have a publish status (if not already trashed).
• Update front-end redirect logic to only act on redirects with publish post status.
• Update tests accordingly.

A future separate issue can then look at the UI and implementation for toggling the active status of a redirect.