[copyright decorator] improve default label string

- Instead of using (c) QGIS YYYY, rely on the project metadata
to insert the author name. It's a more useful default string,
and might help avoid a misconception about ownership of maps
produced in QGIS.

src/app/qgsdecorationcopyright.cpp

@@ -59,14 +59,11 @@ void QgsDecorationCopyright::projectRead()
 {
   QgsDecorationItem::projectRead();
 
-  QDate now = QDate::currentDate();
-  QString defString = "© QGIS " + now.toString( QStringLiteral( "yyyy" ) );
-
   // there is no font setting in the UI, so just use the Qt/QGIS default font (what mQFont gets when created)
   //  mQFont.setFamily( QgsProject::instance()->readEntry( "CopyrightLabel", "/FontName", "Sans Serif" ) );
   //  mQFont.setPointSize( QgsProject::instance()->readNumEntry( "CopyrightLabel", "/FontSize", 9 ) );
 
-  mLabelText = QgsProject::instance()->readEntry( mNameConfig, QStringLiteral( "/Label" ), defString );
+  mLabelText = QgsProject::instance()->readEntry( mNameConfig, QStringLiteral( "/Label" ), QString() );
   mMarginHorizontal = QgsProject::instance()->readNumEntry( mNameConfig, QStringLiteral( "/MarginH" ), 0 );
   mMarginVertical = QgsProject::instance()->readNumEntry( mNameConfig, QStringLiteral( "/MarginV" ), 0 );
   mColor = QgsSymbolLayerUtils::decodeColor( QgsProject::instance()->readEntry( mNameConfig, QStringLiteral( "/Color" ), QStringLiteral( "#000000" ) ) );

src/app/qgsdecorationcopyrightdialog.cpp

@@ -46,8 +46,19 @@ QgsDecorationCopyrightDialog::QgsDecorationCopyrightDialog( QgsDecorationCopyrig
   connect( applyButton, &QAbstractButton::clicked, this, &QgsDecorationCopyrightDialog::apply );
 
   grpEnable->setChecked( mDeco.enabled() );
-  // text
-  txtCopyrightText->setPlainText( mDeco.mLabelText );
+
+  // label text
+  if ( !mDeco.enabled() && mDeco.mLabelText.isEmpty() )
+  {
+    QDate now = QDate::currentDate();
+    QString defaultString = QString( "%1 %2 %3" ).arg( QChar( 0x00A9 ), QgsProject::instance()->metadata().author(), now.toString( QStringLiteral( "yyyy" ) ) );
+    txtCopyrightText->setPlainText( defaultString );
+  }
+  else
+  {
+    txtCopyrightText->setPlainText( mDeco.mLabelText );
+  }
+
   // placement
   cboPlacement->addItem( tr( "Top left" ), QgsDecorationItem::TopLeft );
   cboPlacement->addItem( tr( "Top right" ), QgsDecorationItem::TopRight );