reorganizing project and adding setup.py

Most of the code has been moved into the fbmessengerlib package, and
messenger.py has been renamed to just fbmessenger. The intra-package
imports no longer allow some of the circularity we were relying on, so
all the external method calls have been removed from windows.py.
external.init() is now responsible for binding external objects to the
three windows.
adding a README