misc.sh: use 'hash' in command_exists
xmonad: lots of changes ...

* Add status bars (dzen / conky)
* Add background programs (nm-applet, gnome-keyring, xscreensaver)
* Add startup programs (rxvt, firefox, skype, pidgin, remmina)
xmonad: sorted out workspaces; mouse follows focus
xmonad: add trayer
xmonad: add UrgencyHook
xmonad: moved app startup into xmonad-setup

Prevents apps being relaunched when xmonad is restarted.