messageTimeout default to max value

[rclark]

messageTimeout is an important, but often overlooked parameter. Currently, its default setting is an arbitrarily chosen value (10 minutes). If jobs take longer to process than 10 minutes, and the caller hasn't learned about messageTimeout yet, they get pretty confusing results where jobs are processed more than once.

Instead of this arbitrary 10 min timeout, the default value should be the maximum possible from SQS.

[brendanmcfarland]

In watchbot 4 messageTimeout is now defaulted to 3 minutes. message.heartbeat will keep refreshing the visibility timeout, and maxJobDuration is available as a parameter for limiting how long a message will be processed before the child_process is killed and the message is retried. see #203 & #230