Added support for moon.Header to use multiple background images and positions.
Additional bonus, backgroundSrc may now be set to `null` to remove the property and allow CSS to be written from a stylesheet.
You may even set backgroundPosition to initial or inherit, and those values will be respected instead of assuming you want `background-position: inherit right;`
Enyo-DCO-1.1-Signed-off-by: Blake Stephens <blake.stephens@lge.com>
Code reorganization and simplification.
Merge pull request #1193 from enyojs/BHV-2240-blakestephens

BHV-2240: Added support for moon.Header to use multiple background images and positions