Drag and Drop revamp, fixes to tabbing

The major change in this version is the way in-which drag and drop operates. We are now dispatching the full range of drag events rather than just mouse events. Since this is a significant change in behavior, please let us know if you discover new drag-related issues.

A minor bug has also been fixed around element tabbing, where users could get an IndexOutOfBounds exception if tabbing at the end of the page, or anti-tabbing at the start of a page. Syn now correctly "wraps" focus.

Lots of additional tests have been added as well to lock-down some of this functionality.