Image Annotation Extractor

This pull request adds an ImageAnnotationExtractor that extracts image annotations stored using the ImageAnnotator system on the Commons (https://commons.wikimedia.org/wiki/Help:Gadget-ImageAnnotator), relying on the W3 Media Fragments recommendation (http://www.w3.org/TR/2012/REC-media-frags-20120925/).

It adds two new properties: _resource_ dbo:hasAnnotation _wikipedia image with annotation included_ and _wikipedia image with annotation included_ dbo:asWikiText _string_.

It also closes gaurav#31.