Add opt WithID and GetPID accessor to engine

[koola]

This PR adds the following to engine;

WithID(id string) option (default is random int as string)
GetPID() accessor

Updated example remote to use SendWithSender with engines GetPID.

[tprifti]

The idea of actor framework is that actors should receive messages, and they are identified by PID. The engine itself should not have a PID. The engine is responsible for forwarding messages to actors, so PID does not make sense in engine struct

[koola]

Then think of it as more of a convenience method. It doesn't affect anything which you have stated as a pattern.