List, GroupedList: can listen for scroll changes from the layout to keep scrolling smooth when items unexpectedly resize (references #432)
List: fixed issue where list didn't listen for scroll event from default layout
ILayout: documented event properties on change event
IVariableVirtualLayout: fixed documentation for scroll event
HorizontalLayout, VerticalLayout: now dispatch Event.SCROLL events to adjust scroll position to avoid jumpy or shifting items when scrolling backgrounds while the layout is virtual with variable item dimensions (closes #432)
HorizontalLayout, VerticalLayout: added some missing event docs