title: Set span for items in GridLayoutManager using SpanSizeLookup
body: <p>I want to implement grid-like layout with section headers. Think of <a href="https://github.com/TonicArtos/StickyGridHeaders">https://github.com/TonicArtos/StickyGridHeaders</a></p>
  
  <p>What I do now:</p>
  
  <pre><code>mRecyclerView = (RecyclerView) view.findViewById(R.id.grid);
  mLayoutManager = new GridLayoutManager(getActivity(), 2);
  mLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
              @Override
              public int getSpanSize(int position) {
                  switch(mAdapter.getItemViewType(position)){
                      case MyAdapter.TYPE_HEADER:
                          return 1;
                      case MyAdapter.TYPE_ITEM:
                          return 2;
                      default:
                          return -1;
                  }
              }
          });
  
  mRecyclerView.setLayoutManager(mLayoutManager);
  </code></pre>
  
  <p>Now both regular items and headers have span size of 1. How do I solve this? </p>