Navigate carousel with arrow keys

[andela-johia]

What does this PR do?

• This PR implements navigation of the carousel in the course page with arrow keys.

Description of task completed?

• Identify elements inside the carousel content.
• Activate arrow-keys when user clicks elements not inside the carousel content.
• Deactivates the arrow-keys when user clicks specific elements inside the carousel content.

How to test this feature?

• cd into coursebuilder.
• Run python tests/integration/course_carousel_test.py to test.

Link for live testing?

• https://cfafrica-mooc-dev.appspot.com/test/unit?unit=4