modified FlowLayoutSample to directly utilize FlexLayouts lib
override measure to set the vertical size of the container

call target.invalidateSize() after each element has been positioned
in updateDisplayList. This will force a call to measure where the
container vertical size is calculated based on the number of 'rows'
created by shifting elements down.
remove explicitly set width from the data group to allow height to change

Explicitly setting a controls height will override any internal measure
logic so this had to be removed to allow the height of the container to be
set but the updated FlowLayout.