FredPluginFCPMessageHandler.FCPPluginMessage.constructRawMessage(): Require errorCode & errorMessage; Adapt callers to new signature
- This effectively adds "ErrorCode" and "ErrorMessage" fields to the on-network format. They are not documented in the FCP Wiki yet. Will do this once the branch gets merged
- This only adapts the network format parser class fcp.FCPPluginMessage. What remains is to change the serializer class FCPPluginReply to also put them into the network message.