add a get_normal_artist_name function to try and normalize artist name variations

- add a get_artist_lists function to group artist name variants into a list
- add a get_normalized_artists function to return normalized artist objects
- use the above functions in:
    - searching artists
    - album artists
    - playlist artists

server/app/lib/playlistlib.py

@@ -11,7 +11,7 @@ from app import exceptions
 from app import instances
 from app import models
 from app import settings
-from app.helpers import Get
+from app.helpers import Get, get_normalized_artists
 from app.lib import trackslib
 from app.logger import get_logger
 from PIL import Image
@@ -153,8 +153,5 @@ class GetPlaylistArtists:
     def __call__(self):
         artists = set()
 
-        for t in self.tracks:
-            for a in t.artists:
-                artists.add(a)
-
-        return [models.Artist(a) for a in artists]
+        artists = [a for t in self.tracks for a in t.artists]
+        return get_normalized_artists(artists)