Add test for function to receive key list
RegistrarClient: Add stub implementation of the GetKeys method
Add the kGetPort command for the server's port request
RegistrarClient: Implement the GetKeys function
RegistrarClient: Implement the ReceiveKeys function
Move the DecodeCommand function to the common library
Registrar: Implement the kGetKeys command processing
Registrar: Add the SendKeys method stub implementation
Registrar: Remove the key value from the answer with the assigned port
Reactor: Remove the key message from the answer with data value
Remove the unused IsMsgEqual function
Registrar: Implement the SendKeys method
KeyList: Implement the GetKeys method
Registrar: Fix bug with array of keys packing to ZMQ message
RegistrarClient: Fix bug with array of keys unpacking from ZMQ message
Fix test for the GetKeys method of RegistrarClient class