Make the course catalog page editable in Divi Builder.

### Reproduction Steps

1. Install the Divi 4.21.0 (theme) and LifterLMS 7.1.4.
2. Complete the setup of LifterLMS.
3. Create a test course.
4. Open the course catalog page on the backend. You should [this](https://share.getcloudapp.com/Wnumo4Nv).
5. Click on the **Edit with the Divi Builder** button.
6. You should see something like [this](https://share.getcloudapp.com/eDurGA0E).
7. Compare this to any other LifterLMS pages, like the dashboard, as you can see [in this screencast.](https://share.getcloudapp.com/Wnumo4v1)

### Expected Behavior
1. The course catalog page should be editable from within the Divi Builder, similar to show other LifterLMS pages can be edited.
2. The course catalog page should not look badly styled by default, as you can see in [here](https://share.getcloudapp.com/eDurGA0E)

### Actual Behavior
1. The course catalog page is not editable from within the Divi Builder, unlike how other LifterLMS pages can be edited.
2. The course catalog page looks badly styles, as you can see in [here](https://share.getcloudapp.com/eDurGA0E)

### This issue has been recreated:
+ [x] Locally
+ [ ] On a staging site
+ [ ] On a production website
+ [ ] With only LifterLMS and a default theme

### Other Options
To accomplish the same thing (or close enough), the user can use the **Divi Theme Builder**. See [www.elegantthemes.com/documentation/divi/the-divi-theme-builder](https://www.elegantthemes.com/documentation/divi/the-divi-theme-builder/).

### Other Info
Since this involves the Divi Builder page builder interface, this report might be more appropriately filed to the Divi team, rather than on LifterLMS. But the LifterLMS developers should make final call on whether this is LifterLMS's responsibility or not.