Successful TCP socket connection refactor

[mikaelwills]

Hey guys,

For a work research project we needed a flutter client to connect and use a 3cx server.
3cx unfortunately doesn't allow for a websocket connection.

I've succefully implemented a TCP connection with this package by abstracting a SocketInterface class that two WebSocket, and TcpSocket classes extend. Can register with the 3CX server, make calls, talk successfully and hang up.

I'm reaching out to field the interest in this as a future pull request!

Cheers