This new ui::Style should finally replace the old app::skin::SkinStyle
class. At this moment both implementations are working to avoid an
huge refactor in just one commit.
- Added new ui::Style property in ui::Widget.
- Removed old code to set the button "bevel" (removed
app::setup_bevels() functions).
- Removed setup_look() function and Left/RightButtonLooks.
- Removed check_button_new() function.
- Removed ui::Theme::paintButton/ComboBoxButton() functions.