Move all synchronisation functionalities into an extensions module, so to be optional

[Mec-iS]

I'm submitting a

• [x] feature request.

Current Behaviour:

Socket functionalities automatically run when hydrus is started so it is ready for connections from the agent. Socket is readyed and all the helpers implement a synchronisation call on the socket to communicate with an agent.

Expected Behaviour:

• hydrus should be started as "stand-alone" by default, support for the sync mechanism should be explicitly set to be available.
• Optimally synchornisation should be packaged in an external library to be installed as pip install hydrus-agent-sync.
• To achieve this decoupling, we should have a config variable to be set USE_AGENT_SYNC=false/true if hydrus-agent-sync is installed
• also all the calls to socketio in the handlers should be factorised out in hydrus-agent-sync and called only if the synchronisation is on.

[sameshl]

Great, that you created this issue @Mec-iS. This decoupling was really needed in hydrus.

[chrizandr]

I agree, we want hydrus to be able to work without sync as well. Agent works right now without sync, this could be added here in a similar way