Add super for mro

[rothloup]

Added calls in object init() methods to super() to support python's MRO. Addresses Issue #22.

[davidhamann]

Thanks for the PR. A couple of remarks:

• The added super() in server.py currently uses tabs as indentation, leading to a TabError exception and breaking the code
• We could skip the argument to super(), as self should implicitly be passed (i.e. for example super() vs super(Server, self))
• I would prefer to pass the surplus args only via kwargs to avoid confusion and make it more explicit when using multiple inheritance. What do you think? I'm currently also getting a mypy error for the super calls complaining about the call to object's __init__ with args, but I assume this should be fine as surplus args should already be consumed before the last __init__ call.