Change foreign key references in `leaderboard_*` tables to smallint

[Askaholic]

Does that mean we should changes the primary key of the referenced tables too?

[norraxx]

If we have references in column definition, we have to move references to key/index table definition, below column definitions.

Be aware of integrity errors, if there is inconsistent behavior, we shoudl fix them.
If it won't be possible, use SET FOREIGN_KEY_CHECKS = 0; before migration, and SET FOREIGN_KEY_CHECKS = 1; after migration.
I preffer to fix reference checks.

[Brutus5000]

@Askaholic yes, the reference key column has to match.