Fixes encountered while working on demo app.

Fixes encountered while working on demo app.

* enyo.GridListImageItem
	* Add `centered` property, to allow left-aligning captions by setting false
	* Add `imageSizing` property, facaded to enyo.Image in chrome
	* Add `useCaption` and `useSubCaption` for use with `imageSizing`, to control padding & absolute positioning of captions when `imageSizing` is used

Enyo-DCO-1.1-Signed-Off-By: Kevin Schaaf (kevin.schaaf@lge.com)