Plot Backgrounds on Capabilities Analysis

[k-tatgenhorst]

I submitted an update for ss.ca.r which gives control over the colors.
The plots on the left continue to have a white background when the background color is changed.
It is not horrible, but not optimal. I believe it is related to using viewport without defining a rectange, so
it either needs defined rectangles or perhaps a background can be set in the actual plot.

As this was only a minor aesthetic, I chose to submit as is and address later. If anyone reading this knows, please feel
free to tweak it.

[k-tatgenhorst]

My programming background is in a number of other languages, so I am learning r as I go. That said, right now I am in the middle of a course on ggplot2 and have seen a number of changes which I feel may be useful.
One (which this issue made me think of) is providing an option to allow these functions to output the choice of ggplot objects or png images (current output). Is there any reason not to do this?
Allowing this would allow much greater flexibility with the output including themes etc...