Normalize display of artist names

lib/music_library_web/artist_helpers.ex

@@ -0,0 +1,7 @@
+defmodule MusicLibraryWeb.ArtistHelpers do
+  def format_artist_names(artists) do
+    artists
+    |> Enum.map(fn a -> a.name end)
+    |> Enum.join(", ")
+  end
+end