Blocks: Scroll the page to the inserted block

[youknowriad]

closes #621

Try inserting an image, a text, a button, a separator.
The editor should scroll to the inserted block properly.

[jasmussen]

Works for me! Nice and simple! 👍 👍

[aduth]

From @iseulde's comment at #565 (comment), I thought we might need to try to control TinyMCE's behavior to ensure consistency. But I was finding that this event wasn't being fired. Instead, I think it's just that TinyMCE is also calling focus to the newly initialized content body here:

https://github.com/tinymce/tinymce/blob/8695816/src/core/src/main/js/init/InitContentBody.js#L140

There doesn't seem to be a way to control this and, honestly, I don't think it's going to be terribly disruptive since it seems like it's the Editable and its block wrapper fighting for focus. In either case the user will likely end up where they'd like.

My only concern was whether scroll-by-focus was a browser-specific implementation, but in my brief testing, this appears to behave consistently across Chrome, Safari, Firefox.