Enable Xmonad for XFCE

Enabling Xmonad requires several steps:
1. Disable xfwm4 from the session autostart
2. Create an autostart command to run xmonad --replace
3. Add my personalized xmonad.hs commands (requires extra xmonad packages,
other than the default)

I also added "echo" commands ino the install.sh script just to remind me of
these things