Update xmonad and xmobar configurations

Replaced weather in xmobar with MPD information. Added spacing around
windows in xmonad. Add grid menu for launching applications,
manipulating windows and quiting xmonad. Add other minor layout changes.
Change gtk UI, icon, and cursor theme
Add, and update config files for, powerline
Start gpg-agent automatically with zsh
Switch terminal to st
Update zsh config

Add sudoedit alias. Don't display `detached:' in red when logged in
through ssh.
Use normal blue for git diff filenames
Switch window manager to herbstluftwm

Major UI overhaul. Out with xmonad and in with herbstluftwm! Add custom
configs for hlwm, conky and dzen2.