Add an image sizing mechanism to moon.Icon, like moon.IconButton

Enyo-DCO-1.1-Signed-off-by: Blake Stephens <blake.stephens@lge.com>
Merge pull request #1859 from enyojs/fix-IconSizing-blakestephens

Add an image sizing mechanism to moon.Icon, like moon.IconButton

Reviewed-By: Aaron Tam (aaron.tam@lge.com)
Integrated-By: Aaron Tam (aaron.tam@lge.com)