Also perform several improvements such as PEP8 cleanup,
write complete docstring, type checking of the input arguments,
accepting a full placement to modify the position,
and deprecating the older call.
Update the Gui Command 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.
