Updating pkgDNLs_worldmapcolor

Updating pkgDNLs_worldmapcolor function with ggplot2::aes_string. This restablish the functionnality of the functions (which was returning an error) and is better for the R CMD CHECK.

Also, the 'data' directory of the package is not on the CRAN (but is on the github version of the package). However pkgDNLs_worldmapcolor(...) needs the 'WorldBordersData.RData' file in order to work. So the 'data' folder should be included whenever submitting installr to CRAN.

Cheers,
Boris