Added a need_homed property to the stage ABC to indicate if stages need homing

Author: iandobbie

microscope/abc.py

@@ -1468,6 +1468,27 @@ def axes(self) -> typing.Mapping[str, StageAxis]:
         """
         raise NotImplementedError()
 
+    @property
+    def need_homed(self) -> bool:
+        """Boolean flag to say if the stage needs to be homed. Many stages 
+        need to be driven to their limts at startup to find a repeatable zero
+        position and sometimes to find their limits as well. 
+
+        By default this function returns "False". If the stage needs
+        to be homed then this function should be overwritten to return
+        "True" until the homing operation has been performed.
+        Additionaly a stage that needs to be homed should implement a
+        home() fucntion that performs the home move, sets limits and
+        leaves the stage somewhere sensible.  This function should
+        also set the need_homed propety to False.
+
+        Stages that dont need homing can leave this default function
+        and dont need to implment the home() function.
+
+        """
+        return False
+
+    
     @property
     def position(self) -> typing.Mapping[str, float]:
         """Map of axis name to their current position.