Accepted Solutions
To make a widget you just need to put it into the right "declare" 'shell'. Look at the other widget folders to get an idea of the folder/file structure. I just started doing this a couple days ago and I am a newbie. So for your concept of forward/previous extent, I'd just clone the Home widget folder in stemapp, and then just throw the back/forward JS inside it, like so:
navToolbar = new Navigation(map);
on(navToolbar, "onExtentHistoryChange", extentHistoryChangeHandler);
use dojo to attach click handlers to the two HTML DOM nodes (a back and forward image for buttons):
navToolbar.zoomToNextExtent();
navToolbar.zoomToPrevExtent();
I may end up writing this in the next few days if you don't whip it up or if it isn't already somewhere else, and if so, I'll be happy to post the code here! 
Thanks Kevin just an update that my rate of progress is not in line with 'whip it up' 
at present. I appreciate the tip (and Rickey's) on looking at the folder structure, sample code/widgets and how these interact (now understanding more, very helpful)...But how to structure the code in the widget.js and widget.html vs. this js api sample (below) is not clear, if you have time to assist that would be awesome ....I'm going to keep digging but you're likely to get through it first just a heads up...
thanks
-Nick