💡Save 'outputData' to 'localStorage' on data change (triggered by onChange() event) built-in support

Once the page is reloaded, the data in the Editor.js is lost. How about saving it in the localStorage (or cookies) which would be triggered by onChange() event.

A small element can be used to represent the current state of the data. For example,
`[Saving...] => [Saved]` and this will be triggered by onChange() function internally.
It could also show some error message like `[Not Connected]` for network issues.

I know this can be implemented by the user but a native support would be great! :)

I can start working on the feature, if approved.