Extended Settings do not show on a multi-site install

[donnapep]

Issue Overview

The Extended Settings do not show on a multi-site install.

Steps to Reproduce (for bugs)

1. Install and activate the Sensei plugin on a multi-site install.
2. Click on Lessons > Add New.
3. Notice that the Extended Settings are empty.
4. Repeat steps 1 & 2 on a single site install.
5. Notice that the Extended Settings correctly show the Lesson Prerequisite, Lesson Course, Lesson Preview and Lesson Module sections.

Chrome 62.0.3202.94 on MacOS 10.12.6 and WordPress 5.0-alpha-42389 running Storefront theme, Gutenberg 1.9.0, Sensei 1.9.19. No other active plugins.

Expected Behavior

The Extended Settings for a multi-site install should show the Lesson Prerequisite, Lesson Course, Lesson Preview and Lesson Module sections as they do for a single site install.

Current Behavior

The Extended Settings are empty for a multi-site install.

Screenshots / Video

Multi-Site (Incorrect)

Single Site (Correct)

Todos

• Tests
• Documentation