pilosa.Server now implements StatusHandler and EventReceiver and needs only
start a gossip memberset. A gossip member set now takes a server as an argument
explicitly and the maze of handlers and receivers and the starting sequence is
somewhat simplified.
Server now trivially implements EventHandler by passing the call along to its
Cluster object which has the actual implementation. This means that less things
will need to refer to cluster.
trying to separate internal an external concerns in pilosa.Server - it should
handle Cluster, Holder, etc. while pilosa/server handles things with external
deps - e.g. Logger, Stats, Handler, etc. Using functional options in
pilosa.Server now.
