Fixed dataTransfer.getData/setData to work with IE

IE needs the first argument of dataTransfer.getData/setData to be Text or URL. See: 

http://msdn.microsoft.com/en-us/library/ie/ms536744%28v=vs.85%29.aspx

Fix tested on IE, Chrome and Firefox.
Merge pull request #42 from jacobilsoe/fixes

Fixed dataTransfer.getData/setData to work with IE