BAC-1004: introduce ThemeSettings::getWordmarkUrl()

This method will return up-to-date URL to wiki wordmark defined in ThemeDesigner

Use it in Oasis and WikiaMobile code
BAC-1004: add ThemeSettings::getBackgroundUrl()

This method will return up-to-date URL to wiki background defined in ThemeDesigner

Use it in SassUtil when generating parameters for SASS URLs
ThemeSettings: c&p is evil!
Merge pull request #1969 from Wikia/release-195-bac-1004-theme-designer-swift

BAC-1004:ThemeDesigner does not work with new Swift Storage (affects wikis with short bucket name)