Fix/wizard admin menu priority 3

[ronchambers]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

The original wizards code in trunk gave us the ability to adjust the priority of a wizard's add_page callback. Somewhere in the timeline of the epic/ia development, this ability was hard-code then removed around the time we were fixing the parent menu custom ordering. In the end, after attempt 1 and attempt 2, and lots of discussion, testing and a huddle with @miguelpeixe - we've settled on this PR in order to reinstate the removed code.

Changes:

• The parent menu order variable was renamed to be more descriptive of what it does: $parent_menu_order.
• The reinstated variable for add page priority was give a descriptive name: $add_page_priority.
• The old/hard-coded newspack parent menu was changed to $this->parent_menu so wizards can control which parent menu they are added to.
• Some minimal changes were made to the advertising wizards and the dashboard.

How to test the changes in this Pull Request:

1. Pull this branch on top of epic/ia.
2. Run npm run build if you haven't already for epic/ia.
3. Verify the wp-admin menus are displaying as expected.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

[miguelpeixe]

Thank you for all the discussions and tackling this! It's a nice and comprehensive solution. I left a non-blocking suggestion there, feel free to merge if you disagree.

[miguelpeixe]

I remember we thought of submenu_priority here, but I like this idea better. Following the same logic, the priority is applied to the admin_menu hook, so perhaps it should be called admin_menu_priority. WDYT? This is non-blocking, though.

[ronchambers]

Agreed. I kept going back and forth... $admin_menu_priority is closer to what I had in original PR. Updated.

[ronchambers]

@jaredrethman FYI. If you notice any issues with advertising/sponsors let me know. Thanks!