Integration with PMPro CPT

[ideadude]

Users may be already protecting LearnDash or Lifter CPTs with our PMPro CPT plugin. If PMPro courses is active and those modules are turned on, we should remove the LD and Lifter CPTs from the list considered by PMPro CPT. We want to make sure the "require membership" box isn't added twice and that users are NOT redirected away from course pages... let PMPro Courses handle it.

Basically, if PMPro Courses is active and in use, let that plugin handle course CPTs instead of the PMPro CPT one.