v5.0.0-b3

• Header/Section with new ISectionable item [See #31](still need to add features on this).
• Redesigned the Item interfaces to simplify development and usability.
• Merged the FlexibleExpandableAdapter into FlexibleAdapter.
• mItems is now private and fully synchronized, the new method updateDataSet allows to update full content and notifyChange.
• Auto-mapping of the ViewType (using Layout resourceId) when using implementation of IFlexibleItem interface.
• Possibility to disjoint Creation and Binding of the View Holder in the Model items OR (user choice) to create and bind the view inside the Adapter (as usual).
• 3 new configurations for FlexibleViewHolder in combination with onTouch, selection and ActionMode state.
• Customizable view elevation on item activation [See #38].
• Better implementation of Expandable items.
• Added possibility to have Expandables inside another Expandable. Limits are described.
• Added support for Payload when notifyItemChanged is called (still need to work on this).
• New method addItemWithDelay().
• Use of Log.error instead of Log.warn.
• New options menu for example App for the showcase.