Status command

I busted the Connection about out into it's own module
and added functionality for determining the currently active connection.
I also removed the parse_ifup_output method from Scheme because it was
causing issues (see #43).  In its stead, I am using the capabilities
from the Connection object.

There is now a status command.  Currently the status command itself pretty limited, but there is room for growth.

```sh
$ sudo wifi status
scheme:  home
ssid:    SSID
```

This pull request also addresses #43.