- renames `refSource`, `refMedium` and `refUrl` to `referrerSource`, `referrerMedium` and `referrerUrl` respectively for consistent naming across files and usages
refs https://github.com/TryGhost/Team/issues/1907
- assigns top-level domain as source for external referrers that don't have known mapping
- returns `Direct` as source for new members when no referrer information is found
refs TryGhost/Team#1923
- updates referrer translator logic to use grouping for known domains/urls to calculate source and medium
- returns first external ref url if nothing matches in history in first pass
refs TryGhost/Team#1907
- calculates final attribution source and medium using captured referrer information in history
- adds new referrer-translator that goes through available history and based to determine most valid referrer info
- includes referrer url, source and medium in the attribution data for storage