messageId column is wrong type for messageBody and messageReceive

[mikeholler]

Currently messageBody and messageReceive are auto-incrementing BIGINT unsigned primary keys (messageId). This is incorrect.

messageSend should have the only auto-incrementing primary key of these three tables, as inserting into messageSend determines the messageId for the other two tables. A message should always be inserted into messageSend before either of the other two tables, and this can be enforced by the API.

The solution is to make messageId on messageBody and messageReceive a BIGINT unsigned primary key and foreign key to messageSend.messageId.

This is not a huge bug, and the API is 100% functional without fixing it, but the fix would help the database self-enforce constraints better.