I just followed this document on a Debian Stretch, and it worked out of
the box. So let's use Debian's current stable release here.

Before 7827f896, mandatory hostname field in config mode was
pre-filled with the default hostname.

This commit adds the config_mode.hostname.prefill option for
controlling the default value.

gluon-config-mode-geo-location-osm extends the
gluon-config-mode-geo-location with a location picker based on
OpenStreetMaps.

Based-on-patch-by: Jan-Tarek Butt <tarek@ring0.de>

As already done with other config mode texts, the altitude field now has
default texts that are used when they are not set in the site i18n files.
The altitude-help text has been removed from site i18n; instead, the
geo-location-help text now overrides the whole section description
including the part that mentions the altitude.

With all the packages being built 10GB are not enough anymore.

gluon-config-mode-contact-info: provide enhancements for german, english and french translation to comply with DSGVO (#1394)

* do not allow to obligatorily require contact information
* add remark that the data is provided voluntarily
* mention how to delete the data
* be very clear about the fact that the data being entered is public and
  can be downloaded and processed by anyone.

In multidomain setups, VXLAN is enabled by default, but can be disabled in
domain configs using the mesh/vxlan option. In single domain setups, the
mesh/vxlan option is mandatory.

The UCI option for legacy mode is removed.

Fixes #1364

This setting allows to enforce manually setting a hostname.

In the initial configuration, the hostname field is now left empty; when
setting the hostname is not enforced, the default hostname is shown as the
field placeholder.

Fixes #1139

Also add documentation about config mode settings.