Fix extra quote on external URLs

Rework detection of external URLs to handle more protocols and fix extra
quote character that got into the formatting with last fix, breaking
external url()s in CSS with Firefox.

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@lge.com)
Merge pull request #670 from enyojs/ENYO-3850-unwiredben

Fix extra quote on external URLs