Bugfix SUP-142
When transforming empty block-level elements (e.g. change a paragraph to a pre-element),
the block-level element did not always contain an ending break to make it visible.
This has been fixed.
Also the handling of placeholder paragraphs (landing zones before or after the first/last element
in an editable) has been fixed. If placeholder paragraphs are filled, the classes marking them
as placeholders are removed.
Bugfix SUP-989
Fixed scrolling if editable itself has a vertical scrollbar and
content is added in a way that the selection would be outside of the
visible area.