Adding basic Sauerbraten masterserver, implemented in Twisted.
Its features are:
 - acting as a proxy for another masterserver (sauerbraten.org)
 - offering the default Sauerbraten master list ("addserver ip port")
 - allowing registrations using "regserv"
 - removing servers after 60 minutes, and forcing them to reregister by disconnecting them
 - logging to stderr if run.py is directly called, logging to a file when using twistd
Adding Flask-powered WSGI application as HTTP endpoint.