add foreign keys to db tables

[jennyy-lei]

should probably use foreign keys for match categories, players too. Categories is just stored as a string right now and players are ints.

[choiii-darren]

phase 1: add and populate new columns for players 1.1: add to existing code that use match object to also use player columns 1.2: apply migration in production phase 2: change existing code to use player columns instead of player array phase 3: make migration to remove old columns and refactor code to accept no more player array columns 3.5: also deploy phase 3.0 migration