Implement bounds checking on the message scheduling properties

This task is to implement bounds checking on the message scheduling properties. The values for delay, period  + repeat should be rejected if they are < 0. Also, a maximum value should be set (and configurable) for the max repeat value, as it has the potential to cause a denial of service issue if many messages are sent with a repeat value of Integer.MAX_VALUE. In the accompanying PR, I've set the default max value to 1000.