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

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')

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

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

While we use the hexadecimal representation as a hash input for simplicity,
it should not be interpreted as case-sensitive.

The new proto will simplify the switch to VXLAN encapsulation.

LEDE recently disabled multicast snooping by default:

https://git.lede-project.org/?p=project/netifd.git;a=commitdiff;h=52541140f8138e31958cdc3d7e42a4029fa6bbc9



Reenable it for Gluon as there have been no confirmed issues for
LEDE and no negative reports concerning Gluon v2016.2.x so far.

Closes #1025.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>

In addition, transitive and fixed_mtu now default to 0 instead of an empty string.

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

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

These values have been in use in gluon-core for some time, the validators
need to be moved as well.

Nothing outside the config mode depends on luci-base anymore.