- fixed the Copy Object function when the object is Gerber

- added the Copy entry to the Project context menu
- made the functions behind Disable and Enable project context menu entries, non-threaded to fix a possible issue

FlatCAMGUI.py

@@ -323,6 +323,7 @@ class FlatCAMGUI(QtWidgets.QMainWindow):
         self.menuproject.addSeparator()
         self.menuprojectgeneratecnc = self.menuproject.addAction('Generate CNC')
         self.menuproject.addSeparator()
+        self.menuprojectcopy = self.menuproject.addAction('Copy')
         self.menuprojectdelete = self.menuproject.addAction('Delete')
 
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