External connections page markup enhancements - #550

[joshuaabenazer]

Takes care of #550

Description of the Change

1. Attempt to make markup more consistent with that of default post type listing pages
2. "Add new" is now not part of the title “External connections” and is outside the H1.
3. "<h2 class="screen-reader-text">Filter connections list</h2>" added before filters list.
4. "All" filter is now highlighted

Benefits

Takes care of some issues with accessibility and also keeps a consistent default look for the post type listings across the dashboard

Verification Process

1. Head over to Dashboard -> Distributor -> External connections
2. Compare header and filters markup with that on page wp-admin/edit.php?post_type=dt_ext_connection

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

#550

Changelog Entry

• Fixed - External connections page markup enhancements

[jeffpaul]

This has been tested locally and confirmed passing tests, current check is failing as PR author doesn't have write access to the repo.