Add the notification player

Now when you select a video to play it in the background mode,
appears a notification (for now does nothing).

app/src/main/java/com/github/libretube/BackgroundMode.kt

@@ -4,6 +4,7 @@ import android.content.Context
 import com.github.libretube.obj.Streams
 import com.google.android.exoplayer2.ExoPlayer
 import com.google.android.exoplayer2.MediaItem
+import com.google.android.exoplayer2.ui.PlayerNotificationManager
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.runBlocking
 
@@ -22,6 +23,8 @@ class BackgroundMode {
     private var player: ExoPlayer? = null
     private var playWhenReadyPlayer = true
 
+    private var playerNotificationManager: PlayerNotificationManager? = null
+
     /**
      * Initializes the [player] player with the [MediaItem].
      */
@@ -30,6 +33,15 @@ class BackgroundMode {
         setMediaItem()
     }
 
+    /**
+     * Initializes the [playerNotificationManager] attached to the [player].
+     */
+    private fun initializePlayerNotification(c: Context) {
+        playerNotificationManager =
+            PlayerNotificationManager.Builder(c, 1, "background_mode").build()
+        playerNotificationManager?.setPlayer(player)
+    }
+
     /**
      * Releases the [player].
      */
@@ -60,6 +72,7 @@ class BackgroundMode {
             job.join()
 
             initializePlayer(c)
+            initializePlayerNotification(c)
 
             player?.apply {
                 playWhenReady = playWhenReadyPlayer

app/src/main/java/com/github/libretube/myApp.kt

@@ -1,8 +1,33 @@
 package com.github.libretube
 
 import android.app.Application
+import android.app.NotificationChannel
+import android.app.NotificationManager
+import android.os.Build
 
 class myApp : Application() {
+    override fun onCreate() {
+        super.onCreate()
+
+        initializeNotificationChannels()
+    }
+
+    /**
+     * Initializes the required [NotificationChannel] for the app.
+     */
+    private fun initializeNotificationChannels() {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+            // Create the NotificationChannel
+            val name = "Background Mode"
+            val descriptionText = "Shows a notification with buttons to control the audio player"
+            val importance = NotificationManager.IMPORTANCE_DEFAULT
+            val mChannel = NotificationChannel("background_mode", name, importance)
+            mChannel.description = descriptionText
+
+            val notificationManager = getSystemService(NOTIFICATION_SERVICE) as NotificationManager
+            notificationManager.createNotificationChannel(mChannel)
+        }
+    }
 
     companion object {
         @JvmField