move class HelpMessageBox to guiutil.cpp/.h / add button to show Bitcoin command-line options (in RPC Console -> Information) / resize Debug window a little to allow for a non-breaking display of the welcome message with non-english translation

src/qt/rpcconsole.h

@@ -35,6 +35,8 @@ private slots:
     void on_tabWidget_currentChanged(int index);
     /** open the debug.log from the current datadir */
     void on_openDebugLogfileButton_clicked();
+    /** display messagebox with program parameters (same as bitcoin-qt --help) */
+    void on_showCLOptionsButton_clicked();
 
 public slots:
     void clear();