Refactoring: Moved some code from app.DupeGuru to fs.File.

Moved DupeGuru._get_display_info() to File.get_display_info().
This method used none of the app's global state or methods
and had nothing to do there.

core/fs.py

@@ -145,6 +145,11 @@ class File:
             raise OperationError(self)
         self.path = destpath
     
+    def get_display_info(self, group, delta):
+        """Returns a display-ready dict of dupe's data.
+        """
+        raise NotImplementedError()
+    
     #--- Properties
     @property
     def extension(self):