AbstractSingleton
- class mtf.utils.Singleton.AbstractSingleton
- __init__(name, bases, dct)
 - static __new__(mcls, name, bases, namespace, **kwargs)
 - mro()
- Return a type’s method resolution order. 
 - register(subclass)
- Register a virtual subclass of an ABC. - Returns the subclass, to allow usage as a class decorator.