Switch from custom edit page, to meta boxes on an Add New page

[GaryJones]

Currently, the add new redirect page is found at edit.php?post_type=vip-legacy-redirect&page=add-redirect.

This is created by registering a new admin page, via add_submenu_page().

However, since the purpose of the screen is just to add a new instance of a custom post type (something that WP already supports), we can go about this in a different way.

What we need is to allow the creation of new posts (vip-legacy-redirect), and then register a callback that amends the metaboxes on the page, to add a custom metabox that includes the fields we need.

Among other benefits, would be that the Publish metabox would be visible - this allows the later supporting of scheduled publishing of redirects to make them live, and different redirect statuses. Until this we could likely remove these from the Publish metabox.

• remove the 'create_posts' => 'do_not_allow' capability. This will turn on the Add New button at the top of the Redirects list page (see "Add Redirect" button in All Redirects page #39), and add a new "Add New" page at post-new.php?post_type=vip-legacy-redirect.
• add in methods to register metabox, and provide fields in custom metabox.
• remove existing registration of pages and generated HTML methods.