Implemented application login.

Minor UI improvement.
Fixed memory leaks.

application/logindialog.h

@@ -0,0 +1,29 @@
+#ifndef LOGINDIALOG_H
+#define LOGINDIALOG_H
+
+#include <QDialog>
+
+namespace Ui {
+class LoginDialog;
+}
+
+class LoginDialog : public QDialog
+{
+    Q_OBJECT
+
+public:
+    explicit LoginDialog(QWidget *parent = 0);
+    ~LoginDialog();
+    QString login() const;
+    QString password() const;
+    void reset();
+
+private:
+    Ui::LoginDialog *ui;
+
+    // QDialog interface
+public slots:
+    void accept() override;
+};
+
+#endif // LOGINDIALOG_H