homing: Make homing.py an "extras" module

Move klippy/homing.py to klippy/extras/homing.py and convert the code
to an "extras" modules.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/toolhead.py

@@ -273,8 +273,8 @@ class ToolHead:
                                desc=self.cmd_SET_VELOCITY_LIMIT_help)
         gcode.register_command('M204', self.cmd_M204)
         # Load some default modules
-        modules = ["gcode_move", "idle_timeout", "statistics", "manual_probe",
-                   "tuning_tower"]
+        modules = ["gcode_move", "homing", "idle_timeout", "statistics",
+                   "manual_probe", "tuning_tower"]
         for module_name in modules:
             self.printer.load_object(config, module_name)
     # Print time tracking