Added max concurrent downloads setting

Fixed issue where navigating to a subscription video would make the player behave like a playlist for the whole sub

backend/appdata/default.json

@@ -13,6 +13,7 @@
       "safe_download_override": false,
       "include_thumbnail": true,
       "include_metadata": true,
+      "max_concurrent_downloads": 5,
       "download_rate_limit": ""
     },
     "Extra": {