gluon-core: gluon.util: pass UCI cursor as argument to iterate_radios() instead of using local context

batman-adv 2017.0 doesn't need (or support) no_rebroadcast anymore. Don't
fail when the file doesn't exist.

VPN daemons were always disabled

Doing so caused broken validations, as different validators were affecting
each other.

Based-on-patch-by: Cyrus Fox <cyrus@lambdacore.de>

Based-on-patch-by: Cyrus Fox <cyrus@lambdacore.de>

The fastd_mesh_vpn site.conf section is renamed to mesh_vpn.fastd.

The ebtables rules were not adjusted when switching from macvlan to veth.

rpcd is not included in our images anymore since switching to gluon-web, so
we don't need to disable it anymore.

This makes the LAN port the PoE master, so the AirGateway can be used to
supply power to another node connected via mesh-on-LAN.

Fixes #608

We always want to prefer the unique node address for outgoing traffic. Note
that this doesn't have an effect with batman-adv, as usually br-client will
be the outgoing interface, so the unique address would be chosen anyways.

This was introduced in ffhh-packages at https://github.com/freifunkhamburg/ffhh-packages/tree/master/gluon-config-mode-reboot-ffhh

Make use of our new _translate() function.

_translate() will return nil when no match is found.

The gluon-web package is basically a stripped-down and refactored version
of the LuCI base.

As convenient as the Map is, the underlying code is very complex and will
be removed.

Add translation support to gluon-status-page, including English, German and Russian translations.

Fixes #1043