Align to grid - room for improvement

[will-moore]

The algorithm was improved in #651 but some layouts can still produce unexpected results with "Align to grid".

For now, let's just capture these so we can consider the best improvements to the algorithm and have examples for testing.

These screenshots include a "before" and "after" collection of panels, generated by first duplicating a collection of panels,
and the "Align to Grid" for just the duplicated collection, so as to create the "after":

1. • Bug: "green" panel is not moved:

2. • Bug: panels become overlapping:

[Rdornier]

Another improvement would be to take into account the labels around the panels, to not hide them behind a panel