Code refactoring

- Code refactoring
- Fix a bug that the other player will not become the host of the room at once, when the player disconnect in link play.

> Maybe add many unknown bugs. XD
> The song database `arcsong.db` will not used in the future. You can use a tool in `tool` folder to import old data.

latest version/templates/web/updatedatabase.html

@@ -11,11 +11,11 @@
 </form>
 <div class="content">
     这里可以将旧版本的数据库同步到新版本的数据库，并刷新用户拥有的全角色列表。<br />
-    可上传文件: arcaea_database.db和arcsong.db<br />
+    可上传文件: arcaea_database.db<br />
     新数据库不存在的数据会被添加，存在的重复数据也会被改变。<br /><br />
     Here you can synchronize the old version of the database to the new version of the database and refresh the list of full
     characters owned by players.<br />
-    Uploadable files: arcaea_database.db & arcsong.db<br />
+    Uploadable files: arcaea_database.db<br />
     Data that does not exist in the new database will be added and the existing duplicate data will also be changed.
 </div>
 <br />