use standard git colors

I'm trying to simplify my gitconfig a bit, and these custom colors don't
seem like they add much value. May be weird for a few minutes though. ;)
add global leiningen profile

Specifically this loads the lein-exec plugin as a global, so that I can
use it from any leiningen projects.

https://github.com/kumarshantanu/lein-exec
remove more color stuff from gitconfig
remove explicit master branch reference
change tracking (deprecated) to upstream

This setting allows git to figure out where to push the branch based on
what branch it is set up to track. This helps because names don't always
match up perfectly.
remove pb alias from gitconfig
yolo