homing: Create Homing class from gcode

Create the Homing class in the gcode handler instead of in the
kinematic classes.  This will make it easier to pass error messages
back to the user.

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

klippy/homing.py

@@ -14,13 +14,17 @@ class Homing:
         self.eventtime = 0.
         self.states = []
         self.endstops = []
+    def set_axes(self, axes):
+        self.changed_axes = axes
+    def get_axes(self):
+        return self.changed_axes
     def plan_home(self, forcepos, movepos, steppers, speed):
         self.states.append((self.do_home, (forcepos, movepos, steppers, speed)))
         self.states.append((self.do_wait_endstop, ()))
     def plan_move(self, newpos, speed):
         self.states.append((self.do_move, (newpos, speed)))
     def plan_axes_update(self, callback):
-        self.states.append((callback, (self.changed_axes,)))
+        self.states.append((callback, (self,)))
     def check_busy(self, eventtime):
         self.eventtime = eventtime
         while self.states: