This is preparatory work for adding other connection types to upstream
servers. The service command `network create` now accepts a scheme in
the address flag, which specifies how to connect to the upstream server.
The only supported scheme for now is ircs, which is also the default if
no scheme is specified. ircs connects to a network over a TLS TCP
connection.
Add bouncer logs, in a network/channel/date.log format, in a similar
manner to ZNC log module. PRIVMSG, JOIN, PART, QUIT, MODE are logged.
Add a config directive for the logs file, including a way to disable
them entirely.
