Fixes #146: Load background images with relative url from external stylesheets.
Merge remote-tracking branch 'origin/master' into bugfixes/relative-background-image

Conflicts:
	packages/HTML.package/CSSBackgroundFormatter.class/methodProperties.json
	packages/HTML.package/monticello.meta/version
Merge pull request #147 from SWTI2014/bugfixes/relative-background-image

Fix #146: Relative background image