***Add Color constants to ostd::Color
***Add MouseEntered/MouseExited callbacks
***Fix mouse detection currently using local coordinates
***implement file theme loading
***Implemenmt MouseDragged callback
***Add scissoring to only draw inside the bounds of containers
***Implement Drag And Drop
***Implement a way to determine on what widget (in the hierarchy chain) and event must stop
***Implement const in stylesheet
Add theme caching
Implement mouse scroll callback
Implement margin for widgets
Implement color constants in stylesheet


Implement following widgets:
	***Label
	Button
		Image/Icon
	Panel / Container
		Title Label
	Checkbox
	Radio Button
		Grouping
	Text Input
	Horizontal Slider
	Vertical Slider
	Image / Icon
	ScrollView
	ListBox
	ComboBox
	TreeView
	Save/Open File Dialogs (and folder dialogs)
	Tab Panel