Ref T591, avoid duplicated text message lines

* also consider Qt::Key_Enter (NUMPAD)
* signal returnPressedUnemptyLine
* use signal returnPressedUnemptyLine instead of returnPressed which avoids empty lines

src/blackgui/lineedithistory.h

@@ -19,6 +19,7 @@ namespace BlackGui
 {
     /*!
      * Line edit with history
+     * \details lines are trimmed and empty lines are ignored
      */
     class BLACKGUI_EXPORT CLineEditHistory : public QLineEdit
     {
@@ -37,6 +38,11 @@ namespace BlackGui
         //! Clear the history
         void clearHistory();
 
+    signals:
+        //! Return has been pressed, line is NOT empty (spaces are trimmed)
+        //! \details returnPressed alsofires on empty lines, but those are not in the history
+        void returnPressedUnemptyLine();
+
     protected:
         //! \copydoc QLineEdit::keyPressEvent
         virtual void keyPressEvent(QKeyEvent *event) override;