- fixed a possible issue in Gerber Object class

- added a new tool in Gerber Editor: Mark Area Tool. It will mark the polygons in a edited Gerber object with areas within a defined range, allowing to delete some of the not necessary  copper features
- added new menu links in the Gerber Editor menu for Eraser Tool and Mark Area Tool
- added key shortcuts for Eraser Tool (CTRL+E) and Mark Area Tool (ALT+A) and updated the shortcuts list

FlatCAMObj.py

@@ -1215,7 +1215,11 @@ class FlatCAMGerber(FlatCAMObj, Gerber):
             cw_row = 0
 
         self.marked_rows[:] = []
-        aperture = self.ui.apertures_table.item(cw_row, 1).text()
+
+        try:
+            aperture = self.ui.apertures_table.item(cw_row, 1).text()
+        except AttributeError:
+            return
 
         if self.ui.apertures_table.cellWidget(cw_row, 5).isChecked():
             self.marked_rows.append(True)