VE-1710: Allow VisualEditor to retrieve Venus flavored Parser output after succesfull save

Venus changes to the Parser output are implemented as Parser hooks and enabled only for Venus skin (otherwise those hooks just return). Fortunetely MediaWiki, including API (api.php) allows to specify skin/context by passing its name as "useskin" GET/POST parameter.

https://wikia-inc.atlassian.net/browse/VE-1710
Merge pull request #5590 from Wikia/VE-1710

VE-1710: Allow VisualEditor to retrieve Venus flavored Parser output after succesfull save