Bugfix SUP-1483
When backspace or forward delete was pressed with a selection of exactly one
breadth (eg: a single character selected) inside an editable in block, the whole
containing block would be deleted. This behavior has now been fixed.
Bugfix SUP-1507
Attempting to resize the leftmost margin of a table had caused the resize handle
to be left as an artifact in the document. This problem has now been fixed.