FLAC/CUE: add track tags, covers/images

[davidnewhall]

FLAC/CUE split kinda works, but @kontel has reported a number of different issues with various cue files. We went back and forth until they were all worked out. This is the culmination of that work.

• Fixes Support for splitting single-file FLAC files with cue. Unpackerr/unpackerr#141
• Adds common tags to tracks.
• Looks for .flac file if cue'd .wav file is missing.
• Copies CUE file to output folder. Adds code to avoid recursively trying to extract it again.
• Copies ToC and Tags from source flac to destination flac files.
• Copies Application and Image blocks from source to destination files.
• Writes extracted image (photo) files to disk.
• Converts UTF16 CUE sheets to UTF8.
• Removes escape characters and other specials from written file names (cue/flac split only, but could be implemented elsewhere if needed).
• Improves ability to locate FLAC file when CUE has the wrong name.