Reset settings.json when GUI options are reset

Clear settings.json file and save settings.json.bak file when "Reset Options"
GUI button is pressed or -resetguisettings command line option is used.

src/qt/optionsmodel.cpp

@@ -250,6 +250,9 @@ static void BackupSettings(const fs::path& filename, const QSettings& src)
 
 void OptionsModel::Reset()
 {
+    // Backup and reset settings.json
+    node().resetSettings();
+
     QSettings settings;
 
     // Backup old settings to chain-specific datadir for troubleshooting