Explanation Editor role

[DrewAPicture]

Following the ​Codex Migration status update I posted on make/docs this morning, I think we're finally to a point where more contributors can selectively be given access to the DevHub back-end for migrating curated documentation from the Codex.

That attached patch adds the new role and grants explanation caps to admins, editors, and explanation editors. Explanation editors will still not be able to push explanations live, but they'll certainly be able to create new ones and submit them for review, as well as edit published explanations.

[coffee2code]

In 3607:

developer.wordpress.org: Add explanation editor role.

Props DrewAPicture.
See #1781.

[coffee2code]

In 3608:

developer.wordpress.org: Expose the explanations post type for administration.

• Allow post type to appear in admin menu.
• Assign menu icon.
• Prevent "Explanations" from being listed in the admin bar "New" menu.
• Remove "Add New" from admin submenu.
• Remove "Add New" from head of "Explanations" admin pages.
• Add count of pending explanations to admin menu.
• Prevent access to the admin page for creating a new explanation.

Fixes #1781.

[DrewAPicture]

@coffee2code I think you still need to manually fire the after_switch_theme action so the new role gets added. It's not showing up in the drop-down because it doesn't exist yet :-)

[drewapicture]

In 3661:

developer.wordpress.org: Check if the user can edit an explanation before giving them an edit link in the Toolbar.

See #1534. See #1781.

[coffee2code]

@DrewAPicture: Ah, I did indeed neglect to do so. It's done now. :)