Fixes #558

Fixes #574

docs: Corrected some typos and strange grammar

If the query was via multicast, the response isn't matched by
--state ESTABLISHED,RELATED

This fixes #619

Instead of starting gluon-respondd from a hotplug handler, add a proper
init script. The new init script has a restart_if_running argument which
is now used by the hotplug handler.

gluon-announced and gluon-announce are merged to gluon-respondd.

Added Support for TP-Link WR843ND

Tests done to verify that this worked as intended:
 * checked plattform_info image_name
 * checked primary_mac
 * does appear in ffmap-d3
 * does mesh
 * does fastd-VPN

Also remove the BROKEN check as the UniFi Outdoor Plus support seems to
work fine now.

Fixes #272

add support for ubiquiti airRouter

docs: Update autoupdater.rst

fix typo and express sentence regarding update priority clearer

introduce function to recurse down to the lowest layer-2 interface
corresponding to a given interface.
also re-introduce some of the previously removed input validation plus
some more to protect against glob and path based exploits.

readme: fix typo, improve formatting

Our build process works similarly to the image builder and doesn't support
the generation of initramfs-based images.

Fixes #616

Fixes #614

Fixes #177

Convert site.conf to JSON during build

docs: add D-Link DIR-505 (A1) and Buffalo WZR-HP-G300NH (and remove WZR-HP-G300N, it is not actually supported)

This will allow us to use its content from other languages than Lua as
well.