Warning: appendCallback hook is deprecated

[sarabourdon-rheo]

Hi,
When I add an image block by clicking "+" and selecting image, I get a warning:

`appendCallback` hook is deprecated and will be removed in the next major release. Use `rendered` hook instead

Indeed appendCallback is used here:

image/src/index.js

Lines 256 to 265 in 25d46cd

	/**
	* Fires after clicks on the Toolbox Image Icon
	* Initiates click on the Select File button
	*
	* @public
	*/
	appendCallback() {
	this.ui.nodes.fileButton.click();
	}

You can reproduce it on Editorjs documentation demo: https://editorjs.io/.
It's not a big deal, just a warning in console, but I didn't see any issues already open so I thought I'd mention it.