Core: Switch widget from 'ExpressionLineEdit' to 'ExpressionTextEdit'

+ minor dialog layout adjustments

src/Gui/Dialogs/DlgExpressionInput.h

@@ -111,7 +111,7 @@ private:
                           QString& message) const;
 
 private Q_SLOTS:
-    void textChanged(const QString & text);
+    void textChanged();
     void setDiscarded();
     void onCheckVarSets(int state);
     void onVarSetSelected(int index);