[Twisted-Python] Avoid circullair dependencies.

[Ivanov Maxim]

Some of my logic need protocol to be imoported to be able to send data back.

So when I start app protocol imports my logic (where all data is processed) 
and my logic imports protocol.  Right now I simply pass protocol object as 
argument to constructors, but it seems to be not the best way from my point 
of view. How to solve this problem?