Enh: Disconnect on <CentProvider> unmount

[Vovan-VE]

<CentProvider> does not disconnect before unmount. It's designed to connect once on application init phase.

I wish to use centrifugo on one-two specific pages in SPA admin panel in a project. I want to connect to Centrifugo server on demand and disconnect then it is unneeded.

I believe it is possible with current available interface, but it whould be much appropriate just to add a counterpart for the following lines:

react-cent/src/cent-provider.js

Lines 53 to 55 in ab9b895

	componentDidMount = () => {
	this.cent.connect(this.props.onConnect)
	}

[fortis]

@Vovan-VE hi!

You right, manual control should also be available. I will try to fix it one of these days