Some more cairo conversions
Don't focus a widget when it's not sensitive or ready for becoming focused
Added first SDL->XWT key code conversions
Introduced widget styles.
Added internal sensitivity-changed notifier
Use WidgetStyles for button rendering
Draw a dash border on to the button when it's focused
Fire OnClicked event when a focused button receives a Space/Return key press event
Reset clicked-attribute if the button has been de-sensitized for more consistent behaviour
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