Automate focuser homing

[bgottula]

Automate focuser homing. Homing is a procedure that sets the reported encoder position to zero when the focuser draw tube is fully retracted. Homing may be necessary any time the focuser clutch slips, which will cause the actual position of the draw tube to disagree with the position stored in and reported by the electronics.

Full automation will likely require intentional slipping of the clutch. Read the documentation for the focuser or send a question over to Ron at MoonLite to make sure this won't cause excessive clutch wear.