Combine seperated custom events into one.

Actually, status of drawer could be distinguished with this.open
property.
So, custom event do not need to be seperated into onExpand and
onCollapse.

Enyo-DCO-1.1-Signed-off-by: David Um <david.um@lge.com>
Add more comment to use custom event

Enyo-DCO-1.1-Signed-off-by: David Um <david.um@lge.com>
Merge pull request #342 from DavidUM/davidum

Combine seperated custom events into one.

Reviewed-By: Ben Combee (ben.combee@lge.com)