BHV-4060: Only reflow when necessary (first opening, picker property change).

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>
BHV-4060: Bubble onRebuilt event to trigger reflow.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>
Merge pull request #1354 from enyojs/BHV-4060-aarontam

BHV-4060: Only reflow when necessary (initial expansion, picker property change).

Good work @aarontam. Thanks for optimizing this.