Optionally show rewind/ff buttons on lockscreen

Show additional playback buttons (rewind and fast forward) in the
notification on the lockscreen if the option "Expand Notification" is
enabled.

Fixes #337
Fixes #571

core/src/main/java/de/danoeh/antennapod/core/preferences/UserPreferences.java

@@ -193,6 +193,16 @@ public class UserPreferences {
         }
     }
 
+    /**
+     * Returns true if additional playback buttons should be shown in the notification even when
+     * on the lockscreen
+     *
+     * @return {@code true} if additional playback buttons should be shown, {@code false}  otherwise
+     */
+    public static boolean showAdditionalNotificationButtons() {
+        return prefs.getBoolean(PREF_EXPANDED_NOTIFICATION, false);
+    }
+
     /**
      * Returns true if notifications are persistent
      *

core/src/main/java/de/danoeh/antennapod/core/service/playback/PlaybackService.java

@@ -867,7 +867,13 @@ public class PlaybackService extends Service {
                     notificationBuilder.addAction(android.R.drawable.ic_media_rew,
                             getString(R.string.rewind_label),
                             rewindButtonPendingIntent);
-                    numActions++;
+                    if(UserPreferences.showAdditionalNotificationButtons()) {
+                        // always show the rewind button (even on the lockscreen)
+                        compactActionList.add(numActions++);
+                    } else {
+                        numActions++;
+                    }
+
 
                     if (playerStatus == PlayerStatus.PLAYING) {
                         PendingIntent pauseButtonPendingIntent = getPendingIntentForMediaAction(
@@ -891,7 +897,12 @@ public class PlaybackService extends Service {
                     notificationBuilder.addAction(android.R.drawable.ic_media_ff,
                             getString(R.string.fast_forward_label),
                             ffButtonPendingIntent);
-                    numActions++;
+                    if(UserPreferences.showAdditionalNotificationButtons()) {
+                        // always show the ff button (even on the lockscreen)
+                        compactActionList.add(numActions++);
+                    } else {
+                        numActions++;
+                    }
 
                     if (UserPreferences.isFollowQueue()) {
                         PendingIntent skipButtonPendingIntent = getPendingIntentForMediaAction(