Allow categories fields to be used to populate keywords

[jsunsawyer]

This would be super useful for channel post types as our categories usually clearly define the post.

[jsunsawyer]

On 2nd thought, this is probably a bad idea. There's a lot of overlap in categories and most of our content would have the same keywords.

I think I was just wanting something easy vs accurate!

[khalwat]

Google ignores the Keywords tag anyway. I wouldn't lose sleep over it.