irkerd: Add kwargs handling to pass data to IRCServerConnection.connect

irkerd: Add kwargs handling to pass data to IRCServerConnection.connect

This makes it easy to pass data down the stack:

  Irker() (stored in Irker.kwargs)
  `-- Irker.handle() -> Dispatcher() (stored in Dispatcher.kwargs)
      `-- Dispatcher.dispatch() -> Connection() (stored in Connection.kwargs)
          `-- Connection.dequeue() -> IRCServerConnection.connect()

You can easily add data at every point in the stack (e.g. we add
'target' in Irker.handle()) and pull it back out when that's
appropriate (e.g. we tap 'target' back out in Connection()).  With
this setup we can reduce the number of global variables currently in
use, because it will be easy to pass data like passwords,
nickame-fallback-ness, etc. down to the appropriate level, without the
intermediate levels needing any changes.