ui::Widget: merged ui::Widget::type_info with ui::Widget::Base.

ui::Widget:
	removed ui::Widget::type_info;
	moved ui::Widget::TypeFlags into ui::Widget::Flags as traits.

ui::Widget::Base:
	added type property (from the remains of ui::Widget::type_info);
	reordered properties & ctor parameters.
ui: merged ui::ProtoContainer into ui::ProtoSlotContainer.

ui::ProtoSlotContainer: removed virtual interface (stay tuned).
ui::Widget::Base: added container query interface.