Generate Unique URLs for each code snippet by a user.

Please refer to these links for reference:

• https://github.com/Sikilabs/django-unique
• https://keyerror.com/blog/automatically-generating-unique-slugs-in-django

Student Code-In

• Please add the label SCI for issues that are made during Student Code-In and are meant for SCI participants only.
• Please make a PR to the SCI branch only, contributions to the master branch would not be accepted.