Time class does not follow getter/setter of other messages #2

@damonkohler @stonier

It looks like here at the Time (and Duration) classes that the method to access secs and nsecs does not follow the same pattern as for the rest of the messages:
https://github.com/rosjava/rosjava_bootstrap/blob/hydro/message_generation/src/main/java/org/ros/message/Time.java#L43

It looks like the old way, not the new "getSecs(), getNSecs(), setSecs(0)" method. So when you access it, the code looks like this:

message.getHeader().getStamp().secs

Do we want to add the methods into the Time and Duration classes?