Enhancing fallback referrer

[raphaelbernhart]

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. :)

[electerious]

We already had support for ref, but I've removed it: #169 (comment)

The problem was that it's overwriting the referrer, but I agree that supporting ref is a good idea. Especially because some browsers are sending an empty referrer. I need to check how the current implementation works. It should still use referrer even available. ref shouldn't be able to overwrite referrer.