ENYO-2446: Drag'n'drop in file manager

ENYO-2446: Drag'n'drop in file manager
Related JIRA: https://enyojs.atlassian.net/browse/ENYO-2446

* use of HTML5 "draggable" attribute
* folder node expansion on hold over
* "package.js" update
* DnD cursor shows if drop target is valid or not
* related FileTree accepts to be draggable when used in File manager

Checked on Windows 7 : Chrome, Chrome Canary, FireFox 21, Opera, Safari, IE10
Note: 
* autoscroll currently only works on Chrome, Chrome Canary, Opera
* Opera doesn't provide the right cursor icon as the target is not valid
* Safari doesn't provide the right cursor icon as the target is valid

Ready to be reviewed

Enyo-DCO-1.1-Signed-off-by: Vincent HERILIER vincent.herilier@hp.com