Code refactor, support multiple gateways and non-SAML authentication (#9)

* Code refactor

* Update README.md

GPClient/normalloginwindow.h

@@ -0,0 +1,37 @@
+#ifndef PORTALAUTHWINDOW_H
+#define PORTALAUTHWINDOW_H
+
+#include <QDialog>
+
+namespace Ui {
+class NormalLoginWindow;
+}
+
+class NormalLoginWindow : public QDialog
+{
+    Q_OBJECT
+
+public:
+    explicit NormalLoginWindow(QWidget *parent = nullptr);
+    ~NormalLoginWindow();
+
+    void setAuthMessage(QString);
+    void setUsernameLabel(QString);
+    void setPasswordLabel(QString);
+    void setPortalAddress(QString);
+
+    void setProcessing(bool isProcessing);
+
+private slots:
+    void on_loginButton_clicked();
+
+signals:
+    void performLogin(QString username, QString password);
+
+private:
+    Ui::NormalLoginWindow *ui;
+
+    void closeEvent(QCloseEvent *event);
+};
+
+#endif // PORTALAUTHWINDOW_H