Feature/tlt 318 enroll instructor

- moves Canvas base URL into its own setting so it can be reused outside of the context of the API (e.g. for course site redirects).
- includes .gitignore parameters to support PyCharm IDE development
- Note: this pull request must be actioned for feature TLT-318 to work in the wizard
For production, we don't go against icommons. It should  be 'https://canvas.harvard.edu/'