dawn: add decentralized wifi controller

dawn: add decentralized wifi controller

Dawn is a decentralized WiFi controller.
Just install dawn and the APs will find each other via umdns.
They periodically exchange information about connected clients, wireless
statistics and other needed information. With that, the daemon load
balances clients between different APs through association control.

Further, the daemon exposes through ubus the hearing map and the
complete wireless network overview. The hearing map is the list of all
probe requests seen from a client from all APs that are running the
controller.

Hearing map:
ubus call dawn get_hearing_map

Network overview:
ubus call dawn get_network

Dawn has a graphical user interface called luci-app-dawn. With that, the
load balancing and other useful settings can be controlled.

Signed-off-by: Nick Hainke <vincent@systemli.org>