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.cpp

@@ -109,10 +109,13 @@ RPCConsole::RPCConsole(QWidget *parent) :
 {
     ui->setupUi(this);
 
-#ifdef WIN32
+#ifndef Q_WS_MAC
     ui->openDebugLogfileButton->setIcon(QIcon(":/icons/export"));
-#else
-    // Show Debug logfile label and Open button only for Windows
+    ui->showCLOptionsButton->setIcon(QIcon(":/icons/options"));
+#endif
+
+#ifndef WIN32
+    // Hide Debug logfile label and Open button for non Windows-OSes
     ui->labelDebugLogfile->setVisible(false);
     ui->openDebugLogfileButton->setVisible(false);
 #endif
@@ -326,3 +329,9 @@ void RPCConsole::scrollToEnd()
     QScrollBar *scrollbar = ui->messagesWidget->verticalScrollBar();
     scrollbar->setValue(scrollbar->maximum());
 }
+
+void RPCConsole::on_showCLOptionsButton_clicked()
+{
+    GUIUtil::HelpMessageBox help;
+    help.exec();
+}