Remove notion of connection_handle from Aries state machines

[Patrik-Stas]

• Code in V3 directory should not contain notion of connection_handle as that's something what belongs to higher layers of abstractions.
• Connection handle is being used typically to: send message (maybe more)
• Instead of connection handle, different minimal abstractions necessary to performs these operations will have to be passed - perhaps closures capable of sending message to the right place, some trait object or maybe connection state machine?
• Side effect will be that connection handle won't be part of serialized credential/proof state machines.
• This will be important step toward extracting state aries protocol state machines to independent crate.

[Patrik-Stas]

Implemented by:

#256
#272
#273