title: Border around r dygraphs plot
body: <p>I would like to have a border around my entire dygraphs plot, encompassing the title, axis labels, legend, etc.  After searching, I think I should be able to use the underlayCallback option to do this, but I cannot find an example, and am very new to dygraphs.  Can anyone point me to an example I've missed, or provide me with a bit of general code to draw the border? I have some plots drawn with ggplot2 (non-interactive), and want my dygraphs to look similar.  Many thanks!</p>