Show channel setting in real-time

[BECATRUE]

Feature you want to implement

As there might be several users to control the same channel, we need to synchronize the channel setting.
For this, a client should keep tracking a modification of channel setting, which is offered by /setting/<int:ch>/ WebSocket.

In addition, the operation status for each channel requested by the user would be fetched when the main page is loaded.

How the feature is implemented

We can handle a WebSocket just using WebSocket class.