Added link menu links: rich snippets, html validation, and css validation.
Added menu link for Facebook Debugger.

Finding it common where users report issues when having WordPress SEO and Jetpack installed. The Facebook Debugger comes in handy to check for duplicate or errors with opengraph tags.
Removed the validator link
Merge branch 'pr/298'

Conflicts:
	inc/wpseo-non-ajax-functions.php