Add support for changing the graph grid color.

I build the graphs for the mlpack website and the grid color doesn't show up well on a black background, so this changeset allows me to set the grid color to whatever looks better with the given background color.  Using textColor doesn't always work in my case because it can be too dark.

Also my vimrc auto-deletes spaces from the end of lines, so this also makes those files slightly smaller. :) (most of the diff changes are that, only a few are the actual gridColor support)