Implement some left-over details of moving executions up and down a lifeline that were not already addressed by #404 for issue #70:
when moving an execution to encompass existing message ends on the lifeline, they would be bumped out of the way instead of simply attached to the execution where it ended up
when moving an execution up, padding from the previous interaction fragment of whatever kind on that lifeline wasn't ensured as it was from the next fragment when moving the interaction down
Note that ensuring padding is always done by nudging elements down, whether to make room for an element being moved down (such as an execution in our case) or by nudging down the elements that were moved up into proximity to others. However, there are problems with that nudge implementation that result in some weirdly sloped messages and possibly other layout issues. Those aren't in scope of this issue at hand; there are other issues covering nudge problems, or possibly new ones to be raised.
Implement some left-over details of moving executions up and down a lifeline that were not already addressed by #404 for issue #70:
Note that ensuring padding is always done by nudging elements down, whether to make room for an element being moved down (such as an execution in our case) or by nudging down the elements that were moved up into proximity to others. However, there are problems with that nudge implementation that result in some weirdly sloped messages and possibly other layout issues. Those aren't in scope of this issue at hand; there are other issues covering nudge problems, or possibly new ones to be raised.