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/guiutil.cpp

@@ -3,6 +3,7 @@
 #include "walletmodel.h"
 #include "bitcoinunits.h"
 #include "util.h"
+#include "init.h"
 
 #include <QString>
 #include <QDateTime>
@@ -413,5 +414,39 @@ bool SetStartOnSystemStartup(bool fAutoStart) { return false; }
 
 #endif
 
+HelpMessageBox::HelpMessageBox(QWidget *parent) :
+    QMessageBox(parent)
+{
+    header = tr("Bitcoin-Qt") + " " + tr("version") + " " +
+        QString::fromStdString(FormatFullVersion()) + "\n\n" +
+        tr("Usage:") + "\n" +
+        "  bitcoin-qt [" + tr("command-line options") + "]                     " + "\n";
+
+    coreOptions = QString::fromStdString(HelpMessage());
+
+    uiOptions = tr("UI options") + ":\n" +
+        "  -lang=<lang>           " + tr("Set language, for example \"de_DE\" (default: system locale)") + "\n" +
+        "  -min                   " + tr("Start minimized") + "\n" +
+        "  -splash                " + tr("Show splash screen on startup (default: 1)") + "\n";
+
+    setWindowTitle(tr("Bitcoin-Qt"));
+    setTextFormat(Qt::PlainText);
+    // setMinimumWidth is ignored for QMessageBox so put in nonbreaking spaces to make it wider.
+    setText(header + QString(QChar(0x2003)).repeated(50));
+    setDetailedText(coreOptions + "\n" + uiOptions);
+}
+
+void HelpMessageBox::exec()
+{
+#if defined(WIN32)
+    // On windows, show a message box, as there is no stderr in windowed applications
+    QMessageBox::exec();
+#else
+    // On other operating systems, the expected action is to print the message to the console.
+    QString strUsage = header + "\n" + coreOptions + "\n" + uiOptions;
+    fprintf(stderr, "%s", strUsage.toStdString().c_str());
+#endif
+}
+
 } // namespace GUIUtil