NetworkManager support

My progress so far to get NetworkManager running.

ToDo:

• The rc-update add networkmanager default command doesn't seem to be working
• ifupdown needs to be removed for networkmanager to function completely
• networkmanager forgets the secret keys for the networks
• openrc needs to start udev, wpa_supplicant and networkmanager in the right order.
• udev doest create the interface added events for the wlan interface on boot.