Unicorn Autohoming GCode for Cupcake with Sticky Tray

This is a simplified and more refined version of my prior Unicorn autohoming code.
* I discovered that simple autohoming was good - but that if you don't raise the Z stage before the XY autohome, you can accidentally draw a line on the sticky note.
* I also discovered that bringing the XY stage to the center without having raised the Z stage could run the pen into several sheets of the sticky note. The sticky note pads I'm using aren't the freshest and the bottom ends of the pad are a littl