[arch-general] Add wpa_supplicant to the Group 'Base'

[Neven Sajko]

I agree that wpa_supplicant probably should not be in base, but
it's worth mentioning that base already has many packages not useful
to a lot of people - I for example don't have any of these installed:
dhcpcd jfsutils reiserfstools xfsprogs cryptsetup lvm2 mdadm nano netctl