Fix encoder if a class is passed

[Psykopear]

Our encoder fails if a class is passed as an argument to one of the operators, because we try to call obj.__getstate__(), and the class doesn't pass the self parameter in this case.

That can happen if we want to use a class __init__ method in an operator:

class Device:
    def __init__(self):
        ...
    def update_avg(self, data):
        ...

flow.stateful_map("average", Device, Device.update_avg)

Here we implicitely want to use Device.__init__, but we are passing the class Device itself to the operator. When we try to encode it, we try to call obj.__getstate__(), but that fails since we are not passing an instance.

This fix prevents that by returning the name of the class if the passed object is, in fact, a class