Add custom events indicating changes of drawer's status

Some widget need to prevent onEnd event from animator in enyo.Drawer.
In this case, custom events are required to notify drawer's status

Enyo-DCO-1.1-Signed-off-by: David Um <david.um@lge.com>
Merge pull request #341 from DavidUM/davidum

Add custom events indicating changes of drawer's status

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@lge.com)