New features for FlexboxLayoutManager

• Add a set of find*Position (find(First|Last)(Completely)?VisibleItemPosition) methods to retrieve the positions of the visible view. #217
• Add support for scrollBars #249
• Add support for smoothScrollToPosition #264

Bug fixes

• Child views are not measured properly when they are not visible #262
• Fixes the issue the FlexboxItemDecoration is misplaced upon scrolling #285
• Nested RecyclerView with FlexboxLayoutManager shows only one line #290
• FlexboxLayoutManager doesn't work with payloads #297
• Fixes the issue that the items becoms invisible on the condition as follows #303
  • the first item's visibility is gone
  • the rest of the items (e.g. three in total) have layout_flexGrow attribute set.
  • the second view has layout_wrapBefore attribute set (no items are
    added to the flex line where the gone view is included)

API Changes

• The constructor of FlexboxLayoutManager now requires a Context.

  FlexboxLayoutManager layoutManager = new FlexboxLayoutManager(context);