Change the PK of the URL model to be the default id
Summary
I made a mistake when writing 2.0 and we need to fix it. Currently, the Primary Key of each URL is it's short URL. This is fine in concept as we want each Go link to be unique (as to prevent conflicting Go links). However in #25 (closed) we want users to edit their links including their short link. When this happens, Django creates an entirely new Go link and does not remove the previous link (Required reading: https://docs.djangoproject.com/en/1.10/ref/models/instances/#how-django-knows-to-update-vs-insert). So, we want to instead go back to using the default Primary Key which is simply an id field. Luckily Django creates this for us if we do not specify a Primary Key on our own.
So in short:
- remove the current PK
- find a way for current links to be migrated into this new id PK
- migrate your database
Currently the PK of a URL is its short url
this is bad because we want to modify the short url in an upcoming feature
we need to have the URL model rely on the Django defualt id that it assigns rows