Initial functionality of player items queue

Fix environment objects

Hide video player placeholder on tvOS

Queue improvements

Model/PlayerQueueItem.swift

@@ -0,0 +1,14 @@
+import AVFoundation
+import Foundation
+
+struct PlayerQueueItem: Hashable, Identifiable {
+    var id = UUID()
+    var video: Video
+
+    init(_ video: Video) {
+        self.video = video
+    }
+
+    var playerItems = [AVPlayerItem]()
+    var compositions = [Stream: AVMutableComposition]()
+}