GF-38613: Add SVG image

To prevent copyright issue in image usage, we provede globally
accessible SVG image.

Enyo-DCO-1.1-Signed-off-by: David Um <david.um@lge.com>
Use enyo.Image.placeholder as static value

Previous implementation wouldn't work properly because enyo.Image is usually
a deferred kind, so setting a property directly on the constructor
will actually set it on the wrong item.  Also rewrote comment to make
its usage clearer.

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@lge.com)