v2.8.1

In this release:

• Add getGroups function to Section
• Add draggable item example to main example project
• Fix javadoc of groupie-viewbinding's BindableItem.bind methods to refer to ViewBinding instead of ViewDataBinding (#334)
• Making Kotlin extensions work with all classes extending GroupieViewHolder. (#350)
• Fix the crash when dragging an item to the top/bottom of the list area in main example (#351 )
• Various version updates and unit test maintenance

❤️ Thank you to the contributors of this release: @rayworks , @herbeth1u , @nashcft & @zsoltvilagos