FCPPluginClient.dispatchMessageLocallyToMessageHandler(): Documentation

- Make it clear that the thread which we're talking about is the send()
which called this function, not the sending of the reply
FCPPluginClient: Fix missing semicolon in logging
FCPPluginClient: Improve logging

- When logging stuff about replies, include both the reply and the
original message
- When logging stuff about replies, make it clear that the SendDirection
is the one of the original message