`listening` property in the Server interface

[hacksparrow]

Description / Steps to reproduce / Feature proposal

How about a listening property in packages/core/Server?

This tells whether the server is running and listening for connections or not.

Current Behavior

Server.listening property does not exist.

Expected Behavior

Server.listening is true or false.

See Reporting Issues for more tips on writing good issues

[jannyHou]

Sounds good to me.
And could potentially make the solution for #822 easier.