Update affiliate handling

[bitboxer]

In #99 we added the affiliate logo to the json we expose. Currently the affilate code is a string in the owner database table. We should change it to an real id and reference the affilate datamodel instead.

For this, we need to:

• Add the affiliate_id column to the owner
• In the migration search for the affiliate_code and add assign the right affiliate
• Migrate the production database
• Check the data for affiliate_codes that have no affiliate_id and fix them manually
• Rewrite all places that use the affiliate_code and replace them with the correct new behavior
• Deploy
• 🥳