Adding subitems, Creating new courses

Fixed a couple of small logic errors that prevented the recursive traversing of subitems of Folders and Lessons and that botched the creation of new courses in Canvas. (And, having noticed some flakiness when I repeatedly import into the same test target course in Canvas, I'm changed my debugging code to usually create a new course, rather than import into an existing course.)

Signed-off-by: Seth Battis <SethBattis@stmarksschool.org>