implemented fallback logic for corrupted window layout (#1039)

* fallback logic for corrupted window layout

1. before saving the window-layout a backup will created to avoid corruption due to crashes while saving

2. when starting chatterino and the window-layout file returns and empty window layout (due to corruptio) the backup will be read and the layout will be build from this data

* Update WindowManager.hpp

* used QSaveFile instead of crude custom implementation

* implemented suggested feedback from review

* proper method call

was tired and slightly drunk Kapp

src/singletons/WindowManager.hpp

@@ -54,6 +54,7 @@ public:
     virtual void initialize(Settings &settings, Paths &paths) override;
     virtual void save() override;
     void closeAll();
+    QJsonArray loadWindowArray(const QString &settingsPath);
 
     int getGeneration() const;
     void incGeneration();