add unit test for raw output of model

Enyo-DCO-1.1-Signed-off-by: Cole Davis <cole.davis@lge.com>
added support for updating the previous and current values of computed properties on those hashes for the 'change' event and added unit test

Enyo-DCO-1.1-Signed-off-by: Cole Davis <cole.davis@lge.com>
Merge pull request #480 from enyojs/ENYO-3125

Fix for ENYO-3125: allow computed properties to accurately appear in the previous/changed hashes for 'change' events

Reviewed-By: Ben Combee (ben.combee@lge.com)