Update solarized-dark colorscheme, and add solarized-light

The current solarized-dark color scheme doesn't work properly on _all_ terminals, and in some cases the colors may show wrong. I fixed that, and made it look a little bit more similar to "[mutt solarized](https://raw.github.com/altercation/solarized/master/img/screen-mutt-dark.png)." I also added a complementing light scheme.