ExtractorHTML when a/@href links include the attribute data-remote="true...

...", include that info the viaContext; and in FetchHTTPRequest, when a CrawlURI has data-remote="true", add the http header "X-Requested-With: XMLHttpRequest"; data-remote is a jquery thing that means the url can be requested via ajax in a browser... some urls work wrong without the X-Requested-With header... this is not a great place for a non-generic thing like this, but where else could it go...

*don't merge yet*