Cross-platform "Open debug logfile"

The option to open the debug logfile from the debug window was implemented only for
windows. By using `QDesktopServices::openUrl` it now works on any platform.

src/qt/rpcconsole.cpp

@@ -114,12 +114,6 @@ RPCConsole::RPCConsole(QWidget *parent) :
     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
-
     // Install event filter for up and down arrow
     ui->lineEdit->installEventFilter(this);