[Qt] let OptionsModel::getProxySettings() directly query proxy

- as a proxy set via GUI can be overridden via -proxy, directly query the
  core to get active proxy
- give a warning, if active proxy is not SOCKS5 (needs to be SOCKS5 for
  the Qt networking code to work)
- also remove an obsolete connect() call from optionsdialog.cpp and a
  reference to Bitcoin-Qt (now just GUI)

src/qt/optionsdialog.cpp

@@ -53,7 +53,6 @@ OptionsDialog::OptionsDialog(QWidget *parent) :
     connect(ui->connectSocks, SIGNAL(toggled(bool)), ui->proxyIp, SLOT(setEnabled(bool)));
     connect(ui->connectSocks, SIGNAL(toggled(bool)), ui->proxyPort, SLOT(setEnabled(bool)));
     connect(ui->connectSocks, SIGNAL(toggled(bool)), ui->socksVersion, SLOT(setEnabled(bool)));
-    connect(ui->connectSocks, SIGNAL(clicked(bool)), this, SLOT(showRestartWarning_Proxy()));
 
     ui->proxyIp->installEventFilter(this);
 
@@ -204,7 +203,7 @@ void OptionsDialog::on_resetButton_clicked()
         if(btnRetVal == QMessageBox::Cancel)
             return;
 
-        /* reset all options and close Bitcoin-Qt */
+        /* reset all options and close GUI */
         model->Reset();
         QApplication::quit();
     }