1. Added 4 style demos and 2 func demos for QCheckBox.
2. Added 3 style demos and 2 func demos for QComboBox.
3. Added 3 style demos and 1 func demo for QDial.
4. Added 4 style demos and 6 func demos for QLabel.
5. Added 5 style demos and 3 func demos for QLCDNumber.
6. Added 7 style demos and 4 func demos for QLineEdit.
7. Added 9 style demos and 2 func demos for QProgressBar.
8. Added 10 style demos and 3 func demos for QPushButton.
9. Added 5 style demos and 1 func demo for QSlider.
10. Added 1 style demo and 1 func demo for QSpinBox.
11. Added two themes: white and black.