More batch delete and update

[groue]

This pull request makes it possible to use the deleteAll and updateAll methods with more query interface requests. Generally speaking, requests that are joined, or grouped on a unique key, can now be batch deleted or updated, when previous versions of GRDB would raise a fatal error.

For example:

try dbQueue.write { db in
    // All teams without players
    let request = Team.having(Team.players.isEmpty)
    try request.deleteAll(db)
    try request.updateAll(db, Column("active") <- false)
    
    // All players whose team is inactive
    let request = Player.joining(required: Player.team.filter(Column("active") == false))
    try request.deleteAll(db)
    try request.updateAll(db, Column("score") <- 0)
}