CLC-3646 - Add API to check ability to provide bCourses course site

https://jira.ets.berkeley.edu/jira/browse/CLC-3646

* Renames Canvas::UserProfile as Canvas::SisUserProfile, as it queries by Campus based UID (SIS Login ID), and updates dependent classes.
* Adds new Canvas::UserProfile which queries by Canvas User ID instead of campus based UID, with #login_id method for more direct conversion of Canvas User ID to Campus UID
* Adds Canvas::PublicAuthorizer with #user_currently_teaching? method, with cached value support
* Updates User::AuthPolicy#can_create_canvas_course_site? to use Canvas::PublicAuthorizer#user_currently_teaching?
* Adds CanvasController#user_can_create_course_site as API end-point