Add a basic dialog script for configuring wpa_supplicant.

Features:
* Does not require wpanet service
* Automatically chooses an appropriate dialog version
  dialog, Xdialog, and whiptail are allowed
  To fall back to dialog if Xdialog is detected, run DISPLAY="" wpa_config
* Supports multple network interfaces
* Add network to config file
  -open, WEP, and WPA are supported
  -hidden networks are broken, unless you go through the main "add network"
  interface.