Course tool UI updates

[bennylope]

• Link to Oppia export for a course
• Link to Moodle export for a course
• Link to course creation tool
• When not logged in then users should be asked to log in to create a course
• Users (esp non-logged in users) shouldn’t be able to edit course that aren’t theirs
• Add some explanatory notes/text - on the courses homepage and also on the course creation page itself
• Add navigation to go back to the courses homepage (from the edit course page)