seqBFplot function

Hi Richard,
I included the seqBFplot.R file, which has roxygen documentation. I was not able to compile the corresponding .Rd file.
I also updated the NAMESPACE and the DESCRIPTION file, which now includes ggplot2 as "Suggested" package.

![bildschirmfoto 2014-07-02 um 07 54 26](https://cloud.githubusercontent.com/assets/2391270/3452209/5a9b6420-01ad-11e4-83f4-c5237bf36181.jpg)