support ip and iw, instead of ifconfig, route, iwconfig

WICD should start supporting ip and iw, instead of ifconfig, route, and iwconfig, which are all going to be deprecated.

This should be a 2-step process: first, let the user choose which "system" to use (also check whether it's possible to use ifconfig + iw, or ip + iwconfig -- I think yes); second, completely drop ifconfig/route/iwconfig in favour of the newer and better alternatives.