Don't throw exception when CSRF token not provided.

* This allows us to authenticate via headers for the API.
Show user token on settings page.
Add a button to show/hide auth token.

* Since the token acts as a password for the API it shouldn't
  be out in the open.
Disable commenting on challenges and assignments.
Avoid displaying line numbers for shell commands.
Add titles to each view.
Remove unused features.

* Assignments
* Courses
* Ratings
Update searches view to exclude assignments.
Remove the ratings table.
Remove enrollments.
Remove courses table.
Remove assignments table.
Remove assignments from seeder.
Fix styling for code in markdown.
Merge pull request #23 from atsheehan/remove_unused_features

Remove unused features