This is a squashed commit containing a number of changes:
This is an ajax driven course selector that has searching etc. It can select single, or multiple courses.
Make course selector accept a list of courses to exclude
courseselector - lookup coursename on setValue
Use the get_course_display_name_in_list function to generate the course names
Add a throttle to auto-complete to reduce spamming the server
Do a single query to fetch all the courses in the mform element when validation fails
Fix core course search function to return results when there are less than 2 chars in the query.
Handle setData with an empty array in new course selector
