Create API endpoint to browse all current courses in db

[huonggiangbui]

Is your feature request related to a problem? Please describe.
Now, a user doesn't know if the course they are going to create exists in our database or not. This creates many duplicated courses in the database. We want to have an API endpoint so that students can call the API and see what courses are available in our database.
This issue should be the extension of #8 (so you want to do this issue after figuring out the current structure of the database)

Describe the solution you'd like
Create a new API endpoint to get all the courses in database. The endpoint format should match the current format (i.e. /coa/api/<something>)

[RichardSabol]

Hi, I would like to work on this. Please assign me the issue.

[huonggiangbui]

Please note that this issue depends on #8, so you want someone to resolve that issue first, and then go ahead : )

[pandyah5]

I would also love to work on this issue!