Update .vimrc for Computer Graphics course.

Add glsl highlighting and fix some colours.
Add custom 6x13 font file.

The original 6x13 (Fixed SemiCondensed) seems to cause problemes with
dzen2. This is just an ungly hack to make it work again (long-term
solution is to dump dzen2 in favour for a homebrew solution, but until
then, months are likely to pass, and I don't want to wait that long for
a pretty statusbar).