LP1906058: Course-term map interface only allow reasonable mappings

LP1906058: Course-term map interface only allow reasonable mappings

Different libraries will use different sets of course terms.  In an
academic library context, for example, a consortium may include
libraries with very different start and end dates to their terms/semesters,
different numbers of terms/year, etc.

This commit changes the interface to only allow users to associate
a course with a term from the same library or one of its ancestors.

To test:
1. Create many courses and course terms and many different OUs.
2. On the course list, click "Terms taught".  Associate some courses
and course terms.  Make sure that you aren't able to associate your
course with any course terms that would not be reasonable for the
course's library.
3. Edit a course, and choose the Course terms tab.  Continue to associate
courses and terms, and make sure the mappings are reasonable.

Signed-off-by: Jane Sandberg <sandbej@linnbenton.edu>