exec() is moved to gluon.util.

Some files have received some additional refactoring.

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.

Based-on-patch-by: Cyrus Fox <cyrus@lambdacore.de>

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

We also make use of the boolean support of simple-uci to make scripts
clearer.

Fixes #414

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

It doesn't seem like this mistake had any effect.

Make bandwidth limits unsigned; trim numbers, the validator accepts
trailing whitespace.

The Gluon-specific functions of the gluon-simple-tc package are moved to
gluon-mesh-vpn-fastd.

When rebooting the node in config mode, currently the fastd key is
forcefully displayed in a fixed format. This is confusing in communities
where fastd accepts all keys and no key submission is needed.
Furthermore, some communities might want to personalize the display of
the key (see #387).

This patch moves the displaying <div> from the package's lua file to the
translation files of the sample site configuration and mentiones the
change in the release notes.

This will require site.mk to explicitly pull in the gluon-setup-mode and
gluon-config-mode-core packages.

Die Bezeichnung "Mesh-VPN" ist etwas irreführend. Man kann denken, dass hiermit das Meshing aktiviert wird, wobei es ja — im Gegenteil — um eine Nutzung des WAN geht.

This commit splits gluon-config-mode into several, mostly independent
packages.

* gluon-config-mode-core: basic functionality (required)
* gluon-config-mode-hostname: hostname field
* gluon-config-mode-autoupdater: show when autoupdater is enabled
* gluon-config-mode-mesh-vpn: fastd vpn configuration, bw limit
* gluon-config-mode-geo-location: geo coordinates
* gluon-config-mode-contact-info: contact info field

The package gluon-config-mode has been removed. You need to replace
it with these packages (or any subset of them) in site.mk:

* gluon-config-mode-hostname
* gluon-config-mode-autoupdater
* gluon-config-mode-mesh-vpn
* gluon-config-mode-geo-location
* gluon-config-mode-contact-info

Note: It is not possible to deactivate the autoupdater in config mode
anymore (expert mode will still allow it). Instead, a message is shown
in case the autoupdater is enabled.