Updated logic of animation code by defining default implementations of onStart, onComplete, and onCancel.  Modified existing widget animations to take advantage of the new code.

Patch by: jlabanca, scottb
Review by: jat, kelly



git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@2900 8db76d5a-ed1c-0410-87a9-c151d255dfc7