Add a few improvements:

- fix QTextEdit background color
- add QTabBar close button style
- improve QDockWidget close button style
Add QTabWidget to example
Improve QToolButton, QCheckBox and QRadioButton
A few more improvements:

- remove outline (button, radio, checkbox)
- remove focus border on radio button
- better hover/pressed state for list view and tree view
Better disabled buttons
Update example with a disabled button
Add examples screenshots
Remove cross on checkbox pressed