gluon-mesh-batman-adv-core: neighbours.d/wifi: output empty object instead of empty list when there are no neighbours on an interface

The file promotes the probably unnecessary re-execution of the announce
scripts. Instead, gluon-announced should be queried using

    gluon-neighbour-info -d ::1 -p 1001 -t0 -r nodeinfo

if both gluon-announced and gluon-neighbour-info are present. But to not
depend on any of those, no script for this one-liner is provided.

By not executing all scripts from gluon.announce themselves, both should
be considerably faster and lighter on RAM usage.

Add support for Ubiquity Air Gateway

gluon-mesh-batman-adv-core: make gateway selection class configurable

Fixes #401

By calling collectgarbage() at various places I was able to reduce heap
usage by ~270kb.

collect_dir() will now pre-load all files and return a function that will
collect all information.

This patch adds the kernel modules to for the very common Realtek RTL8150 and Realtek 8152 based USB-to-Ethernet converters.
After this patch the following packages can be added to targets (or site.mk):
kmod-usb-net-rtl8150
kmod-usb-net-rtl8152

The modules are already available in openwrt trunk, but not in Chaos Calmer. This patch is just a temporary backport.
The modules are needed for Futros with additional USB-Ethernet-Interface and VMs with dedicated USB-NIC

gluon-mesh-batman-adv-core: prepare for 802.11s mesh

The expert mode can still be useful without any cohfig mode modules.

Use the same image for sysupgrade on WZR-HP-AG300H and WZR-600DHP, but use
different factory images.

Add an optional third argument to the GluonProfile macro while contains the
OpenWrt profile name. This allows creating different Gluon profiles (with
different image names etc.) from the same OpenWrt profile.

This reverts commit 8ad3c881.

We can't use the same image for these two devices, so as a workaround,
remove ZR-600DHP from the name for now, so the autoupdater can work and
users aren't confused.

contributing: mention "rejected features" wiki page

Add support for WHR-HP-G300N

Add support for TP-Link TL-WA901ND v1

gluon-luci-private-wifi: typo seperaten

Using a loop makes the script a bit nicer, and it works around a git bug
corrupting patch dates when multiple patches are applied at once.

Add support for x86-xen_domu target

contrib/sigtest.sh - testing signature