Black theme update (#673)

* Playlist already added song prevention & AndroidSlidingUpPanel repo Update

* Update color for black theme, now playing card to have a black color with some radius

app/src/main/res/layout/fragment_flat_player.xml

@@ -100,6 +100,7 @@
                     android:id="@+id/player_panel_content"
                     android:layout_width="match_parent"
                     android:layout_height="wrap_content"
+                    android:background="?cardBackgroundColor"
                     android:orientation="vertical">
 
                     <View