luci-app-dawn: add luci app for dawn

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.

Luci-app-dawn is the graphical user interface.
It allows to:
- Configure dawn
- View Wireless Network Overview
- View Hearing Map

The hearing map is the list of all probe requests seen from a client
from all APs that are running the controller.

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