Support fetching cover art images from the Cover Art Archive

Add option `--cover-art` to `whipper cd rip` command which accepts three values:
- `file`: save the downloaded cover image as standalone file in the rip folder (named `cover.jpg`)
- `embed`: embed the download cover image into all the ripped audio tracks (no standalone file will be kept)
- `complete`: save standalone cover image as standalone file and embed it into all the ripped audio tracks (`file` + `embed`)

Every cover art is fetched from the Cover Art Archive as JPEG thumbnail with a maximum dimension of 500px.
Other supported values for the thumbnails are 250, 500 and 1200 (currently only some images have a corresponding 1200px sized thumbnail).

This feature introduces an optional dependency on the `Pillow` module which is required for the decoding of the cover file (required by the `embed` and `complete` option values).

Problem:
- EmbedPicTureTask shouldn't be a task.

Signed-off-by: ABCbum <kimlong221002@gmail.com>
Co-authored-by: JoeLametta <JoeLametta@users.noreply.github.com>
Signed-off-by: JoeLametta <JoeLametta@users.noreply.github.com>

whipper/common/program.py

@@ -27,6 +27,7 @@ import re
 import os
 import time
 
+from tempfile import NamedTemporaryFile
 from whipper.common import accurip, cache, checksum, common, mbngs, path
 from whipper.program import cdrdao, cdparanoia
 from whipper.image import image
@@ -470,6 +471,35 @@ class Program:
         stop = track.getIndex(1).absolute - 1
         return start, stop
 
+    def getCoverArt(self, path, release_id):
+        """
+        Get cover art image from Cover Art Archive.
+
+        :param path: where to store the fetched image
+        :type  path: str
+        :param release_id: a release id (self.program.metadata.mbid)
+        :type  release_id: str
+        :returns: path to the downloaded cover art, else `None`
+        :rtype: str or None
+        """
+        cover_art_path = os.path.join(path, 'cover.jpg')
+
+        logger.debug('fetching cover art for release: %r', release_id)
+        try:
+            data = musicbrainzngs.get_image_front(release_id, 500)
+        except musicbrainzngs.ResponseError as e:
+            logger.error('error fetching cover art: %r', e)
+            return
+
+        if data:
+            with NamedTemporaryFile(suffix='.cover.jpg', delete=False) as f:
+                f.write(data)
+            os.chmod(f.name, 0o644)
+            os.replace(f.name, cover_art_path)
+            logger.debug('cover art fetched at: %r', cover_art_path)
+            return cover_art_path
+        return
+
     @staticmethod
     def verifyTrack(runner, trackResult):
         is_wave = not trackResult.filename.endswith('.flac')
@@ -490,7 +520,7 @@ class Program:
         return ret
 
     def ripTrack(self, runner, trackResult, offset, device, taglist,
-                 overread, what=None):
+                 overread, what=None, coverArtPath=None):
         """
         Ripping the track may change the track's filename as stored in
         trackResult.
@@ -516,7 +546,8 @@ class Program:
                                            offset=offset,
                                            device=device,
                                            taglist=taglist,
-                                           what=what)
+                                           what=what,
+                                           coverArtPath=coverArtPath)
 
         runner.run(t)