Added support for multiple slaves

[mvkvl]

Changed base Client interface to pass slaveId as an argument to all the methods, to allow communication with multiple slaves on a bus in on session. Mainly this is required for ENC (encapsulated RTU over TCP) mode, when we access a bus via TCP-gateway. Previous implementation required us to establish new TCP session for each slaveId, now we can establish one TCP session and communicate with multiple devices.

[mehmetali10]

It works well. Thank you for your contribution!