first working system test

this PR includes a first working example of a system wide test. Its rather simple:

1. creates a fake client
2. creates a fake server
3. connects both the fake client and the fake server together via StringTransport classes (instead of real TCP as the reactor would do), this is what I consider "starting" the proxy
4. and finally checks that StarryPy forwards the servers PROTOCOL_VERSION packet to the client

To be honest: I opened PR at this point mostly because it has some more-than-minor changes in server.py (+ some other files) that I would like to not have merging issues with in the future whenever we work on these tests