[Matthias Schiffer: slightly clean up code]

[Matthias Schiffer: rebase]

Without -v, hexdump would sometimes replace duplicate bytes with "*" and
a newline.

To reduce the number of packages that need to be listed in
GLUON_SITE_PACKAGES, this adds a new variable GLUON_FEATURES. Sets of
packages are enabled automatically based on the combination of listed
feature flags.

Site-specified package feeds can provide their own feature flag
definitions.

As PROVIDES can be used to replace real packages now, we don't need the
virtual packages as workaround anymore. This also means that the providing
packages don't need to be added to site.mk explicitly anymore when the
default provider is used.

The next-node MAC address doesn't need to be unique in different
communities, so we can as well add a default value.

The SSID for the mesh network should be cryptic, otherwise some users will try to connect to that network and have a bad user experience.

iptables will be pulled in anyways.

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

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

Generate flashable images for the Archer C7 v2 with current stock firmware
again.

To set the region code, the GLUON_REGION variable must be set to "us" or
"eu" in site.mk or as a make argument.

Fixes #860

Allows weird release numbers, models and site names, and prepares support
for pretty hostnames.

and add documentation