Fix guessing of wireless device

The wireless/ directory is still present, while its contents are gone,
as this particular sysfs interface has been deprecated for a while now
Fix wifi signal strength meter

We can get it from iwconfig like we do the essid; sysfs interface is gone
Merge pull request #23 from luka-n/master

Fix wifi module. Thanks so much! I don't know when I would be able to get this otherwise!