functional-tests: Rename extractor tests to show file formats more clearly

Each filename now contains the file format that is being tested as the first item. This should help developers when you want to see at a glance which extractors are being tested by which test cases.

Combined with !98 (merged), the list of extractor tests now looks like this:

tracker-miners:extractor+audio / mp3-id3v2.4-1
tracker-miners:extractor+audio / mp3-id3v2.3-empty-artist-album
tracker-miners:extractor+audio / mp3-id3v2.4-2
tracker-miners:extractor+office / psgz-doc
tracker-miners:extractor+audio / vorbis
tracker-miners:extractor+images / jpeg-basic
tracker-miners:extractor+images / jpeg-region-of-interest
tracker-miners:extractor+images / jpeg-iptc-tags
tracker-miners:extractor+images / jpeg-iptcdata-records
tracker-miners:extractor+images / gif-comment-extension-block
tracker-miners:extractor+images / gif-corrupted-image
tracker-miners:extractor+images / gif-xmp
tracker-miners:extractor+images / png-basic
tracker-miners:extractor+images / png-region-of-interest
tracker-miners:extractor+images / tiff-basic
tracker-miners:extractor+images / raw-cr2
tracker-miners:extractor+playlists / playlist-test-1
tracker-miners:extractor+office / oasis-doc
tracker-miners:extractor+office / office-doc
tracker-miners:extractor+office / powerpoint
tracker-miners:extractor+office / pdf-doc
tracker-miners:extractor+office / ps-doc
tracker-miners:extractor+office / ps-doc-atend
tracker-miners:extractor+video / mov-basic
tracker-miners:extractor+video / mp4-basic
tracker-miners:extractor+video / mp4-video-without-audio