Further work on typicalItem replacing typicalItemWidth and typicalItemHeight. Added resetTypicalItemDimensionsOnMeasure to go back to better 1.0.x behavior while still allowing 1.1.x behavior of resetting typical item dimensions. fixed some issues with caching in vertical and horizontal layouts
List, GroupedList: stability fixes for typicalItem used by layout. GroupedList: removed typicalHeader and typicalFooter, since they aren't used anymore.