Using fake file system repo for local course development

Would it make sense to add a course setting, which enables file system fake repo for the course? It could be, for example, a path to a course directory. I think it's useful for course development on a local instance of relate, so that author can work with uncommitted changes and commit them only after previewing it and making sure it works and looks ok on the local instance.

Some naive solution: `get_course_repo` function could return `FileSystemFakeRepo` object if the course directory is specified.

Perhaps it's already achievable somehow. If so, please point me out to a solution.

Thank you!

Start by locating get_course_repo and the existing FileSystemFakeRepo implementation, then check how course settings select a repository. Confirm whether a course-directory setting can support local uncommitted changes and previewing; done means the local instance uses that directory without requiring commits.

Written by the indexing model from the issue text.