Code quality updates for 2.4.0 (#2709)

* Minor code quality fixes found by Codacy
* Fix unused variables when WITH_XC_NETWORKING is OFF
* Fix #2684, resolve entry references from the root group
* Fix #2697 and Fix #2699, listen specifically for 
WM_QUERYENDSESSION and WM_ENDSESSION on 
Windows to gracefully shutdown KeePassXC
* Cleanup proxy code and add explicit closure for
shutdown messages

src/browser/NativeMessagingBase.h

@@ -53,7 +53,7 @@ protected slots:
 protected:
     virtual void readLength() = 0;
     virtual bool readStdIn(const quint32 length) = 0;
-    void readNativeMessages();
+    virtual void readNativeMessages();
     QString jsonToString(const QJsonObject& json) const;
     void sendReply(const QJsonObject& json);
     void sendReply(const QString& reply);

src/browser/NativeMessagingHost.h

@@ -32,7 +32,7 @@ class NativeMessagingHost : public NativeMessagingBase
 
 public:
     explicit NativeMessagingHost(DatabaseTabWidget* parent = nullptr, const bool enabled = false);
-    ~NativeMessagingHost();
+    ~NativeMessagingHost() override;
     int init();
     void run();
     void stop();