Merge nacli and netctl-auto

As requested in gandro/netctl-auto-cli#1, this pull request contains a rewrite of the `netctl-auto` script, essentially adding a command line interface to control the automatic profile selection. The commands are the same as those of `nacli`.

In addition to the new commands, I've also documented the `start` and `stop` commands in the man page. As stated there, these commands are not supposed to be called by the user, but by systemd through the `netctl-auto@.service` unit. Nonetheless I've reworked some of `nacli`s code to work even if `netctl-auto start` was invoked directly. Please let me know if should remove the commands from the documentation.