Add module for json serialization

The module contains wrapper functions around json dumps and loads, and
named tuples to simplify communication between threads.
Add convenience methods to serialization.py

To avoid long expressions such as
serialization.serialize(serialization.Request(...)) create convenience
methods s_req and s_res to automatically create a named tuples and
serialize.
Add basic file server functionality

The file server runs in its own thread and is controlled via a pipe.
It binds a frontend socket in which the actual files will be served.
Currently it listens for file names in a json request and dumps the
whole content in one send.