Add WEP security key support

Not sure this is the best way to handle WEP right now, since there are lots of other security methods, and we're using the AUTO mode by default it seems.   But here's a start.  Let me know what you think.  (also have a pull request open in the gainspan library, here:  https://github.com/Pinoccio/library-gainspan-s2w/pull/8)