[cuegui] Add toggleable option to save settings on exit (#1612)

**Link the Issue(s) this Pull Request is related to.**
#1601 

**Summarize your change.**
This adds an option (which is enabled by default) to save window
settings on exit.

This enables one to save a setup which is the same no matter if you
close the windows 1-by-1 or all at once.

cuegui/cuegui/MainWindow.py

@@ -86,6 +86,10 @@ def __init__(self, app_name, app_version, window_name, parent = None):
         self.setAnimated(False)
         self.setDockNestingEnabled(True)
 
+        # Create checkable menuitem
+        self.saveWindowSettingsCheck = QtWidgets.QAction("Save Window Settings on Exit", self)
+        self.saveWindowSettingsCheck.setCheckable(True)
+
         # Register this window
         self.__windowOpened()
 
@@ -138,7 +142,9 @@ def handleExit(self, sig, flag):
         """Save current state and close the application"""
         del sig
         del flag
-        self.__saveSettings()
+        # Only save settings on exit if toggled
+        if self.saveWindowSettingsCheck.isChecked():
+            self.__saveSettings()
         self.__windowCloseApplication()
 
     @staticmethod
@@ -293,6 +299,10 @@ def __windowMenuSetup(self, menu):
         changeTitle.triggered.connect(self.__windowMenuHandleChangeTitle)  # pylint: disable=no-member
         menu.addAction(changeTitle)
 
+        # Menu Bar: Window -> Save Window Settings on Exit
+        self.saveWindowSettingsCheck.triggered.connect(self.__saveSettingsToggle)  # pylint: disable=no-member
+        menu.addAction(self.saveWindowSettingsCheck)
+
         # Menu Bar: Window -> Save Window Settings
         saveWindowSettings = QtWidgets.QAction("Save Window Settings", self)
         saveWindowSettings.triggered.connect(self.__saveSettings)  # pylint: disable=no-member
@@ -402,9 +412,6 @@ def __windowOpened(self):
     def __windowClosed(self):
         """Called from closeEvent on window close"""
 
-        # Save the fact that this window is open or not when the app closed
-        self.settings.setValue("%s/Open" % self.name, self.app.closingApp)
-
         # pylint: disable=bare-except
         try:
             self.windows.remove(self)
@@ -456,7 +463,9 @@ def closeEvent(self, event):
         @type  event: QEvent
         @param event: The close event"""
         del event
-        self.__saveSettings()
+        # Only save settings on exit if toggled
+        if self.saveWindowSettingsCheck.isChecked():
+            self.__saveSettings()
         self.__windowClosed()
 
     def __restoreSettings(self):
@@ -472,6 +481,15 @@ def __restoreSettings(self):
         self.move(self.settings.value("%s/Position" % self.name,
                                       QtCore.QPoint(0, 0)))
 
+        self.saveWindowSettingsCheck.setChecked(self.settings.value("SaveOnExit", "true") == "true")
+
+    def __saveSettingsToggle(self, checked):
+        """Toggles saving window settings on exit"""
+
+        # Make sure that it has the same state in all windows
+        for window in self.windows:
+            window.saveWindowSettingsCheck.setChecked(checked)
+
     def __saveSettings(self):
         """Saves the windows settings"""
         logger.info('Saving: %s', self.settings.fileName())
@@ -480,6 +498,15 @@ def __saveSettings(self):
 
         # For populating the default state: print self.saveState().toBase64()
 
+        # Save the fact that this window is open or not
+        for windowName in self.windows_names:
+            for window in self.windows:
+                if window.name == windowName:
+                    self.settings.setValue("%s/Open" % windowName, True)
+                    break
+            else:
+                self.settings.setValue("%s/Open" % windowName, False)
+
         self.settings.setValue("Version", self.app_version)
 
         self.settings.setValue("%s/Title" % self.name,
@@ -491,6 +518,8 @@ def __saveSettings(self):
         self.settings.setValue("%s/Position" % self.name,
                                self.pos())
 
+        self.settings.setValue("SaveOnExit", self.saveWindowSettingsCheck.isChecked())
+
     def __revertLayout(self):
         """Revert back to default window layout"""
         result = QtWidgets.QMessageBox.question(