Complete refactor of Browser Integration classes

* Removed option to attach KeePassXC to the browser extension. Users must use the proxy application to communicate with KeePassXC.
* Significantly streamlined proxy code. Used same implementation of stdin/stdout interface across all platforms.
* Moved browser service entry point to BrowserService class instead of NativeMessagingHost. BrowserService now coordinates the communication to/from clients.
* Moved settings page definition out of MainWindow
* Decoupled BrowserService from DatabaseTabWidget
* Reduced complexity of various functions and cleaned the ABI (public vs private).
* Eliminated BrowserClients class, moved functionality into the BrowserService
* Renamed HostInstaller to NativeMessageInstaller and renamed NativeMessageHost to BrowserHost.
* Recognize XDG_CONFIG_HOME when installing native message file on Linux. Fix #4121 and fix #4123.

tests/gui/TestGuiBrowser.h

@@ -45,6 +45,7 @@ private slots:
 
     void testEntrySettings();
     void testAdditionalURLs();
+    void testGetDatabaseGroups();
 
 private:
     void triggerAction(const QString& name);
@@ -57,10 +58,7 @@ private:
     QPointer<DatabaseTabWidget> m_tabWidget;
     QPointer<DatabaseWidget> m_dbWidget;
     QSharedPointer<Database> m_db;
-    QByteArray m_dbData;
     QScopedPointer<TemporaryFile> m_dbFile;
-    QString m_dbFileName;
-    QString m_dbFilePath;
 };
 
 #endif // KEEPASSXC_TESTGUIBROWSER_H