[Combined Fragment:016]: Reorder a combined fragment

It SHALL be possible to reorder a combined fragment by dragging it upwards or downwards while holding the CTRL key. The combined fragment, any actual gate, the attached messages and its related fragment will be removed from the actual location and inserted along the lifelines at the vertical position of the new location, maintaining their relative positions.

The gaps left between the previous fragment and the moved fragments will be closed by shifting up the element along the lifelines an amount equivalent to the height of the gap.

Existing element along the lifelines will be shifted down by an amount equivalent to the height of the whole group.