PyCommand utilizes Object and EventObject parameters

### Description

Currently PyCommand ignores the Command class' Object and EventObject parameters. This prevents doing things like interrogating the EventObject or the callback Object.

### Expected behavior

PyCommand passes Object and EventObject parameters to the user-specified Python callback.

### Actual behavior

PyCommand ignores Object and EventObject parameters from the Command.

### Additional Information

I started to implement allowing for both argument-less callbacks (the current case) and additionally callbacks that would take the Object and EventObject parameters. Where I'm stuck is how to convert the Object * and EventObject & into their SWIG/Python equivalents before calling PyEval_CallObject. For example,

```
void
PyCommand::PyExecute(Object * o, const EventObject & ev)
{
// make sure that the CommandCallable is in fact callable
if (!PyCallable_Check(this->m_Object))
{
// we throw a standard ITK exception: this makes it possible for
// our standard Swig exception handling logic to take this
// through to the invoking Python process
itkExceptionMacro(<< "CommandCallable is not a callable Python object, "
<< "or it has not been set.");
}
else
{
PyGILStateEnsure gil;

PyObject * result = nullptr;
if (GetNumberOfArgs(this->m_Object) == 0)
{ // the callback takes 0 arguments
result = PyEval_CallObject(this->m_Object, (PyObject *)nullptr);
}
else
{
PyObject * args = PyTuple_Pack(o,ev); <<<<<<<<------ how to get o, ev into Python objects
result = PyEval_CallObject(this->m_Object, args);
Py_DECREF(args);
if (result)
{
Py_DECREF(result);
}
else
{
// there was a Python error. Clear the error by printing to stdout
PyErr_Print();
// make sure the invoking Python code knows there was a problem
// by raising an exception
itkExceptionMacro(<< "There was an error executing the "
<< "CommandCallable.");
}
}
}
```

I checked out itkPyImageFilter.h but it seems like it skirts around this issue.