Define the concept of a 'federation Query'; creating API for making and handling Queries on the Federation's increasingly-inaccurately-named ReplicationLayer

Handle a potential race in the notifier when calling get_events_for which resulted in an uncaught KeyError

Use strings instead of opaque magic-number constants for presence states; rename AWAY to UNAVAILABLE

Added a -w flag which will host the web client if specified. Currently this just delegates to the webclient RestServlet.

add in copyrights to everything, not just the synapse subdir, and add a copyrighter.pl whilst we're at it