- CGI script and index.html are moved from gluon-web to
  gluon-config-mode-core, the script is renamed to 'config'
- gluon-web and gluon-web-model base views and i18n files are symlinked
  into the new path
- gluon-web-theme is renamed to gluon-config-mode-theme and installs
  directly into the new path
- all gluon-web-* models, controllers and views are moved into the new
  path

exec() is moved to gluon.util.

These files are already located in /lib/gluon, no need to add it a second
time.

Allow returning functions in addition to the names of UCI packages to
commit. Functions are run after all packages have been committed.

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.

Make use of our new _translate() function.

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.

Don't fork reboot process before all package hooks have been handled and
rendering is complete.

Replace debug.setfenv hack to close stdout with nixio.dup.

Fixes #772

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

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

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.