List, GroupedList, PickerList: made selectedItem/selectedItems behave the same with empty data providers or no selected indices (closes #749). List: added getSelectedItems() with optional result vector to avoid allocation/gc
HorizontalLayout, VerticalLayout: added property to distribute item sizes (to allow TabBar to support equally sized tabs)
ButtonGroup, TabBar: re-added support for distributed tab/button sizes (closes #673)
Merge branch 'master' of github.com:joshtynjala/feathers