Fix crash when clearing build plate

We shouldn't delete the singleton PrintInformation object. We should rather just zero out the print information. And instead of doing that explicitly in deleteAll, listen to scene changes from PrintInformation in order to keep the logic related to the print information contained within its class.

Contributes to issue CURA-4810.

cura/CuraApplication.py

@@ -1061,9 +1061,6 @@ class CuraApplication(QtApplication):
             op.push()
             Selection.clear()
 
-        Logger.log("i", "Reseting print information")
-        self._print_information = PrintInformation.PrintInformation()
-        
         # stay on the same build plate
         #self.getCuraSceneController().setActiveBuildPlate(0)  # Select first build plate
 

cura/PrintInformation.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2017 Ultimaker B.V.
+# Copyright (c) 2018 Ultimaker B.V.
 # Cura is released under the terms of the LGPLv3 or higher.
 
 from PyQt5.QtCore import QObject, pyqtSignal, pyqtProperty
@@ -65,6 +65,7 @@ class PrintInformation(QObject):
         self._backend = Application.getInstance().getBackend()
         if self._backend:
             self._backend.printDurationMessage.connect(self._onPrintDurationMessage)
+        Application.getInstance().getController().getScene().sceneChanged.connect(self.setToZeroPrintInformation)
 
         self._base_name = ""
         self._abbr_machine = ""
@@ -171,7 +172,7 @@ class PrintInformation(QObject):
     def printTimes(self):
         return self._print_time_message_values[self._active_build_plate]
 
-    def _onPrintDurationMessage(self, build_plate_number, print_time, material_amounts):
+    def _onPrintDurationMessage(self, build_plate_number, print_time: Dict[str, int], material_amounts: list):
         self._updateTotalPrintTimePerFeature(build_plate_number, print_time)
         self.currentPrintTimeChanged.emit()