Feature for course sections

[kimcoleman]

Is your feature request related to a problem? Please describe.
Long courses often have sections that group similar course content. These can also sometimes be called modules. This helps long courses stay organized and supports learners reaching smaller milestones along the way "you've completed module 2".

Describe the solution you'd like
Let's consider a way to add sections so that lessons are grouped. This could be done from the metabox where lessons are added to the course. We do not need a new CPT or a new landing page / screen on the frontend for a section.

We could optionally support section as an attribute of some shortcodes, but not needed. This is more of a visual grouping than navigational.