Merge pull request #2 from floribon/master

Cross-browser dataTransfer property 
Issue between browsers fixed. Using native event-handlers now.
Update dragandrop.js

Removed jQuery self execution to native one.
Better MCV pattern

+ "on-drag" class added or removed instead of hard-coded opacity for
elements being dragged (opacity moved to css file)

+ jQ-lite addClass and removeClass instead of pure js string
concatenation (makes jQuery addClass break)

+ when-drop function returns the target element as a second optional
parameter