New Settings: Do Not Discovery At Startup

[lferrandis]

Add a new settings, that should be manage by the Manager Interface:

Discovery: True/False

At launch:
If True, the server will launch the discovery of servers
If False, the server will not launch the discovery of servers.

When changing the settings:
False->True: Launch the discovery (and save the settings)
True/False: Stop the discovering, release all devices and save the settings.