As core defines basic rules for this zone, it makes sense to create it
there.

Based-on-patch-by: Christof Schulze <christof.schulze@gmx.net>

OUTPUT is always accepted, no need to allow ICMPv6 explicitly.

Wrap long lines.

 * gluon-core, gluon-client-bridge: introduce new firewall zone: local_client
 * gluon-core: put clients in local_client zone, introduce drop-zone,
   set dns-rules and zones
 * gluon-respondd: allow respondd on mesh
 * gluon-status-page-api: allow http input on mesh and client

Fixes #1269

Filtering by MAC address won't filter out multicast packages like router
solicitations, causing uradvd to send out router advertisements with
maximum frequency (every 3 seconds) in active meshes, even when no local
client is actually interested in the advertisements.

Fixes #1230

by moving the declaration of ret to the top of get_fastd()

The older busybox-based wget erroneously accepted URLs without protocol.
Add validator to avoid building firmwares with broken autoupdates.

Some files have received some additional refactoring.

In particular, this affects users of gluon.util.iterate_radios.

The new gluon.site lua library will eventually replace gluon.site_config
(which is hereby deprecated, but will continue to be supported for a
while).

The new gluon.site library will wrap all values to allow traversing
non-existing tables without errors.

    site = require 'gluon.site'
    c = site.a.b.c -- doesn't fail even if a or a.b don't exist

The wrapped values must be unwrapped using call syntax:

    site_name = site.site_name()

Using the call syntax on a non-existing value will return nil. An
alternative default value may be passed instead:

    mac = site.next_node.mac('16:41:95:40:f7:dc')

simple-uci will now delete an option when nil is passed.

simple-uci will now delete an option when nil is passed.

simple-uci will now delete an option when nil is passed.

simple-uci will now delete an option when nil is passed.

uci:set_list() will delete the list when nil is passed, so there is no need
to differentiate between the cases.