Feature/filetypeextractor

Added a FileTypeExtractor that can extract basic information about Commons files. This required moving the Image URL generation code from the ImageExtractor into ExtractorUtils.
That doesn't change the RDF representation, but OMG does it ever simplify @70d5a09249c -- that can just use a single URL for every single file type! However, the big problem remains: getFileURLAndThumbnail(...) will always return a valid fileURL, but not always a sensible thumbnail. I'm thinking of splitting it into two functions: `def getFileURL(WikiTitle, Language) = {language.baseUri}/wiki/Special:FilePath/{WikiTitle.encoded}`, and `def getThumbnailURL(WikiTitle, Language) = {language.baseUri}/wiki/Special:FilePath/{WikiTitle.encoded}?width=300`. Then it'll be up to the callee to figure out whether WikiTitle refers to an image or not: ImageExtractor should know this already, and FileTypeExtractor will figure this out from the extension. There isn't really a downside, since getThumbnailURL will always return a workable URL.