Create a new menu entry for the configured content types

Problem/Motivation

From the parent issue #2957179: Changes to node add link handling:

When I installed this module I am seeing a message next to my content type name in the "Add content" menu. I understand the motivation behind this addition, but it's producing a pretty long link that I doesn't really seem the best place for the link.

Proposed resolution

Remove the add link for that content type from the "Add content" menu entirely and create a new menu item beneath it called, something like "Single page content". This link would show a list of the content types configured to use Only One. Clicking the link for a content type would take the user to the create/edit page as needed.

Remaining tasks

Create the patch.

User interface changes

A new menu entry will can be create in the Content menu (depends on the module configuration)

API changes

None.

Data model changes

None.