msgr/async: huge refactoring of protocol V1

msgr/async: huge refactoring of protocol V1

This huge commit extracts the protocol V1 logic from the AsyncConnection
class into its own class called ProtocolV1.
The new protocol class extends from a Protocol base class that defines
an interface to allow the implementation of different wire protocols
in the future, such as the msgr V2 protocol.

Signed-off-by: Ricardo Dias <rdias@suse.com>