implement a new method of interacting with bit-server: node-pty

[davidfirst]

Until now we supported two methods to communicate with cli-server: SSE and TTY. See server-commander.ts for more details.

With this approach, we spawn a pty (pseudo terminal) process to communicate between the client and the server.
The client connects to the server using a (TCP) socket. The server writes to the socket and the client reads from it.
The client also writes to the socket and the server reads from it. See server-forever.ts to understand better.
In order to pass terminal sequences, such as arrow keys or Ctrl+C, the stdin of the client is set to raw mode.
In theory, this approach could work by spawning a normal process, not pty, however, then, the stdin/stdout are non-tty, and as a result, loaders such as Ora and chalk won't work.

With this new approach, we also support terminating and reloading the server. A new command is added bit server-forever, which spawns the pty-process. If the client hits Ctrl+C, this server-forever process will kill the pty-process and re-load it.