use a data object for control port info

In ticket:14271#comment:16, arthuredelstein said: In torbutton.js, we will now have

var m_tb_control_socket_file = null; // Set if using a UNIX domain socket.
var m_tb_control_port = null;        // Set if not using a socket.
var m_tb_control_host = null;        // Set if not using a socket.
var m_tb_control_pass = null;
var m_tb_control_desc = null;  

I imagine it might be cleaner to collect these into a single data object like

var m_tb_control = { socket_file, host, port, password, descriptor }

Then we could factor out a single factory function from torbutton_init() that generates this object. And we could use this object as a single argument for functions in tor-control-port.js and tor-circuit-display.js as well.