Changes with Aloha.Editor 1.2.28

Bugfix SUP-1395

When doing drag&drop of blocks in tables, the table cells were also
selected when hovering over them. Also empty table cells were not marked
as possible drop target (although dropping worked).
Both issues have been fixed.

Bugfix SUP-1403

Drag & drop of blocks in tables could interfere with resizing of table cells.
This will be prevented now.

Bugfix SUP-1406

Drag & drop of blocks sometimes caused a JavaScript error,
which will be prevented now.