Class refactoring.

The classes JSONRPC, RequestHandler and System were joined in client.py file for
better organization. I also update the tests and init file.
Media classes refactored.

As the last commit, I'm moving and grouping some classes for the sake of
organization. Nothing big deal, I will also add some useless documentation in he
next commit.
client.py documentation.

As promised, I'm adding some documentation, isn't tested yet, I still have to
update Sphinx.