Inserting a new block should scroll to that block

[mtias]

Whenever you insert a new block using the header + button, we ought to scroll to the bottom so the new block is in view.

[jasmussen]

Actually shouldn't it insert the block where the caret is?

[mtias]

Good point. We should focus the viewport on the newly created block, regardless of where it is inserted.

[jasmussen]

See also conversation in #565 (comment)

Current issue: If you insert a text block (any text, including heading, list, etc.), it scrolls to the inserted block. Good! If you insert a block that doesn't have Editable, like embed or image, it doesn't scroll to the block. Let me know if I should ticket this separately.

A thought from @aduth:

It might be that TinyMCE is scrolling the page when it initializes, in which case we should try to disable that default and implement a consistent approach across all blocks.

A comment from @iseulde:

Saw this the other day: https://github.com/tinymce/tinymce-dist/blob/4.6.0/changelog.txt#L6