PROTON-615: Fix binding dependencies

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1605624 13f79535-47bb-0310-9956-ffa450edef68
made event categories map one to one to context type; split local/remote state events into distinct open/close and remote_open/remote_close events
make the connection's collector reference a weakref in python, and make collectors 'weak' in C
added pretty printing for disposition types