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.
This is the base class of most Draft Gui Commands,
particularly those which were developed a long time ago.
It is inherited by `Creator` and `Modifier`
to set some specific options for some tools.
Newer Gui Commands do not use these classes and thus
are independent of `DraftTool`.
Nevertheless, in the future we expect to organize further
the commands so that they all derive from a few classes,
so that they all share some common properties and behaviors.
