Redirects: show/use new fields

[stsewd]

We have added new fields to redirects that may be shown in the UI, or used to implement some filtering, new fields are:

• Description
• HTTP status code
• Enabled
• Position

ref #237, readthedocs/readthedocs.org#10881

[stsewd]

There was also a discussion around how we can show each type of redirect with the new syntax we have (*, :splat), and Clean/HTML redirects.

#237 (comment)

[agjohnson]

The redirect listing and form view show these fields, think we can close this.