The displacement is added to the position already defined by
the point, in order to impart an additional shift in the copy.
The rotation is also added to the original shape's rotation
by multiplying the quaternions.
Implement `onDocumentRestore` to add the new property
to older objects.
Test the inputs to the `make_point_array` function
and return `None` if there is a problem.
Now the make function accepts as input a `"String"` which must be
the `Label` of an object in the document, so it is easier to create
arrays quickly from the Python console.
Add a message deprecating the older call `makePointArray`.
Adjust the GuiCommand accordingly. Now it uses the commit
mechanism of the parent `Modifier` class so that the executed
functions are recorded in the Python console.
Clean up the `PointArray` class as well.
