Improve cover upload input

- Enable drag and drop (invisible)
- Show upload progress
- Add relevant tests

test/support/fixtures/records_fixtures.ex

@@ -31,7 +31,11 @@ defmodule MusicLibrary.RecordsFixtures do
     "Thick as a Brick"
   ]
   # While it would be great to have this random, it's ok to use one single image
-  @cover_data_path "#{__DIR__}/marillion-marbles.jpg"
+  @marbles_cover_data_path "#{__DIR__}/marillion-marbles.jpg"
+  @raven_cover_data_path "#{__DIR__}/steven-wilson-raven.jpg"
+
+  def marbles_cover_fixture, do: @marbles_cover_data_path
+  def raven_cover_fixture, do: @raven_cover_data_path
 
   def record_fixture(attrs \\ %{}) do
     musicbrainz_id = Ecto.UUID.generate()
@@ -41,7 +45,7 @@ defmodule MusicLibrary.RecordsFixtures do
       |> Enum.into(%{
         genres: Enum.take_random(@genres, :rand.uniform(3)),
         cover_url: "https://coverartarchive.org/release-group/#{musicbrainz_id}/front",
-        cover_data: File.read!(@cover_data_path),
+        cover_data: File.read!(@marbles_cover_data_path),
         musicbrainz_id: musicbrainz_id,
         title: Enum.random(@titles),
         type: :album,