This PR adds a configuration that allows direct redirection from the course home to any course page.
*JIRA tickets*: TDB.
*Sandbox URL*: TBD - sandbox is being provisioned.
*Merge deadline*: None.
1. Checkout this branch.
1. Set `course_experience.unified_course_tab` on [WaffleFlag settings](http://localhost:8000/admin/waffle/flag/).
1. Go to a course's main page and check that it redirects to /course page with the unified course experience.
1. Disable the WaffleFlag, and add the following variable to the [SiteConfiguration Settings](http://localhost:8000/admin/site_configuration/siteconfiguration/):
1. Check if navigating to a course's home page redirect's to the courseware (http://localhost:8000/courses/course-v1:edX+DemoX+Demo_Course/).
1. Test changing that setting to `info`, `about` and `course`, and assert that the correct redirection are made.
1. Set `COURSE_HOME_BEHAVIOUR` to `thisdoesntexist` and check that the page defaults to the original behaviour (showing the course info page) and logs a warning to the console.
*Author notes and concerns*:
1. I'm not sure `SiteConfiguration` is the best place for this setting.
2. This function is partially covered by tests, I can create more unit tests if required.
[ ] @xitij2000
[ ] edX reviewer[s] TBD