gluon-config-mode: mention reboot on button

Make it clear that saving settings will reboot the device.
gluon-config-mode: modularize wizard

This splits up the wizard into modules.
config-mode: split 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: autoupdater flag
* 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

gluon-config-mode is now a virtual package, that depends on

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

to provide the same functionality as the non-modularized config mode.
Communities are free to replace gluon-config-mode in their site.mk with
any subset of the above packages.
config-mode: split reboot page

Render reboot page from fragments in /lib/gluon/config-mode/reboot/.

Each script is expected to return a function, that will eventually
render a template, or nil.
cm-autoupdater-info: autoupdater state

This packages lets the user know whether the autoupdater is enabled when
in config mode.