feat: task file manage (#196)

1. support view task file list
2. support share file on android and iOS

ui/flutter/assets/locales/zh_CN.json

@@ -29,7 +29,7 @@
   "downloadDirValid": "请选择下载目录",
   "connections": "连接数",
   "maxRunning": "最大下载数",
-  "items": "@count 条",
+  "items": "@count 项",
   "subscribeTracker": "订阅 Tracker",
   "subscribeFail": "订阅失败，请检查网络或稍后重试",
   "update": "更新",