add a metadata cache and re-compute ignore when deleting a course to speed up the whole thing as well as squelching warnings in the console output
add same optimizations to the clone course command
rename clone.py to a more descriptive clone_course.py
Merge pull request #570 from edx/fix/cdodge/add-metadata-caching-to-delete-course

Performance enhancements for django-admin commands to delete and clone course