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.
KML is a weird format to deal with anyway: it exists as a separate file (e.g. https://commons.wikimedia.org/wiki/File:First_Manassas_map2.jpg/overlay.kml), it doesn't do thumbnails, but is in the File:... namespace. We should put in an exclusion to skip it, should we exclude all File:... subpages, or have an ignore list in FileTypeExtractorConfig.