title: RecyclerView expand/collapse items
body: <p>I want to expand/collapse the items of my recyclerView in order to show more info. I want to achieve the same effect of the <a href="https://github.com/tjerkw/Android-SlideExpandableListView" rel="noreferrer">SlideExpandableListView</a>. </p>
  
  <p>Basically in my viewHolder I have a view that is not visible and I want to do a smooth expand/collapse animation rather than set the visibility to VISIBLE/GONE only. I only need an item to be expanded at a time and it would be cool to have some elevation to show that the item is selected.</p>
  
  <p>It is the same effect of the new Android recent calls history list. The options "CALL BACK" and "DETAILS" are visible only when an item is selected.</p>
  
  <p><img src="https://i.stack.imgur.com/wcfmX.jpg" alt="RecyclerView expandable items"></p>