gluon-mesh-batman-adv: announce MAC of mesh ifaces

This will make a node announce all MACs of its interfaces participating
in the batman-adv mesh. This enables other nodes to associate the
announced object with both the data reported by batadv-vis as well as a
simple list of neighbours as output by `iw dev $IFACE station dump`.
gluon-announced: send nodeinformation on request

This is a simple daemon that will respond to multicast UDP packets
containing the keyword "nodeinfo" with all the information we
currently distribute using alfred.

The daemon will listen on all mesh interface, that is the hard
interfaces batman-adv uses.
Merge branch 'mesh-announce-interfaces' of https://github.com/freifunk-gluon/packages
Merge branch 'gluon-announced' of https://github.com/freifunk-gluon/packages
Move essential firewall rules from gluon-firewall to gluon-core and gluon-mesh-batman-adv

The now empty gluon-firewall is removed.
gluon-mesh-batman-adv: fix mesh config script
gluon-luci-admin: allow removing all SSH keys
gluon-luci-admin: support disabling password login again
autoupdater: try URL ${BRANCH}.manifest before manifest

This will allow storing different manifests for multiple branches in a single
directory.
UI for enabling a private WLAN [WIP]

freifunk-gluon/gluon#122