Some drag and drop code refactor:

1) Adding DragOptions to easily extend drap functionality
2) Changing onDragStarted signature to send more information
3) Updating states for dropTargetButton based on drag event directly
4) Removing folder item based on onDragStarted and not startDrag

Change-Id: I65b684e092ddc081d086bfe2c8c1973ed170eaeb