Make MAX_COURSES_IN_CATEGORY configurable

Check sort order:

1. Install a new site.
2. Check the current number of categories:
   `select count(id) from mdl_course_categories;`
   • We call it "NUM_OF_CAT".  If it is a fresh install, the  NUM_OF_CAT will be "1" (only Miscellaneous category)
   • We will use "NUM_OF_CAT" to calculate sort order values for categories and courses)
3. Set $CFG->maxcoursesincategory = 20000 in config.php
4. Create 2 categories: Category A and Category B
5. Check the sort order of these two categories:
   `select name, sortorder from mdl_course_categories;`
6. Verify:
   • The sortorder for Category A equals 40000
   • The sortorder for Category B equals 60000
7. Create 2 courses in Category A: Course 1 and Course 2
8. Check the sort order of these two courses:
   `select fullname, sortorder from mdl_course;`
9. Verify
   • The sortorder of course 1 is equal to 40002 (Sort Order Of Category A + 2)
   • The sortorder of Course 2 is 40001 (Sort Order Of Category A + 1)