Integrate OpenMesh devices available in OpenWrt Chaos Calmer:

 - MR600
 - MR600v2
 - MR900
 - MR900v2
 - OM2P
 - OM2P-HS
 - OM2P-HSv2
 - OM2P-LC
 - OM2Pv2
 - OM5P
 - OM5P-AN

Signed-off-by: Sven Eckelmann <sven.eckelmann@open-mesh.com>

Device information can be found at:
http://www.8devices.com/products/carambola-2
https://wiki.openwrt.org/toh/8devices/carambola2

I only did some minimal testing of gluon on the carambola 2 development
board:

 - Config mode works
 - Connects to Wifi Mesh
 - Allows clients to connect

Notably, autoupgrade has not yet been tested.

Change to 010-primary-mac is necessary as the mac address printed
on the sticker is the one of eth0, not the wifi mac.

Newer versions of Sphinx would break lines at the colons.

OpenWRT now supports the CISCO Meraki enterprise class routers
MR12, MR16, MR62 and MR66. The fabric firmware demands the yearly
renewal of a support license.

This firmware was successfully tested by @Garunda for the MR62 (and
the MR12 with it for which this is an alias). The initial firmware
pre OpenWRT adoption was prepared and adapted for Gluon by @tcatm.
The confirmation of the functionality of the image for the MR66
(and the aliased MR16 with it) is still pending.

The devices are of strategic interest to the Freifunk community as
they are making a rock-solid impression. However, these come with
fairly hefty annual license. The Freifunk may offer an escape route
for those who had signed up and want to keep their investment into the
similarly expensive hardware. Used evices sell for $60 on eBay/Amazon
in the US. Here in the old world it is all >300 €, still.

Credits go to @Garunda for testing, to @tcatm for finding the
OpenWRT patch prior to its adoption and preparing the initial Gluon
adaptation, to @smoe for the update once that patch had arrived in
OpenWRT, and to @NeoRaider for his review and advice to use
GluonModelAlias for MR62 and MR66 to point to MR12 and MR16,
respectively.

link to site-repo updated

The Hornet UB is sold at least in the varieties. Without case it is a Hornet UB, with case and without connected USB port it is called AP121. If the USB port is present this device is called AP121U.
We have a AP121U in our mesh http://meshviewer.chemnitz.freifunk.net/#!v:m;n:00c0ca6efffa

This CPE is supported by OpenWRT and already running in Chemnitz

This new feature introduces the new uci section 'gluon-core.wireless' with a preserve_channels option:
 * preserve_channels (boolean)

By setting this option to 1 (true) wifi channels will be preserved during upgrades.

Change the limit to match our recommendation in the site-example.

Fixes #574

fix typo and express sentence regarding update priority clearer

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