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.
In Python 3 `super()` can be used without an argument
in order to get the parent class, `super()`.
In Python 2 the present class must be used as an argument,
`super(ThisClass, self)`.
This commit is done to support Python 2,
as without it all Gui Command tools will be broken
and will fail to launch, even if the unit tests pass.
Also, set the `__metaclass__` variable to `type`.
This is done to turn all classes into "new style" classes
in Python 2. This is required so `super()` works correctly
in this version of Pyton.
This commit can be reverted once Python 2 support
is completely dropped, and only Python 3 compatible code
is used.
