Enhancing fallback referrer

**Problem**
As many apps refer via a referrer parameter in the url called `ref` but ackee uses `source` as the parameter this leads to many refs untracked.

**Solution:**
Create a alias of the `source` param called `ref` so if any app referrs via the `ref` param it will also get tracked.

Ik that there is a fallback referrer but this does not catch all refs.

I see if I have some spare time to create a PR. :)

Start by locating the handling of the existing `source` URL parameter and the fallback referrer logic. Confirm how an alias named `ref` should be accepted and verify that referrals using it are tracked the same way as `source`, using any relevant project tests or tracking flow available there.

Written by the indexing model from the issue text.