Allow Network Manager to use WPA Supplicant Config file

Network Manager(for gnome and KDE) should be allowed to simply select a wpa_supplicant config file, and work with it, as an alternative to the GUI based config wizard. This will make it easier for people already on wpa supplicant(provided by uni's etc...) to migrate to network-manager and also, for options not available on the GUI based config(such as MSCHAPv2 etc...)