Various changes and moving stuff around.

This will free about 5 to 12 MB of RAM even on lightly used devices
yielding plenty of RAM for autoupdate to succeed.

Configmode should be exited by using the wizard instead.

This commit adds gluon-luci-core, a package both gluon-config-mode and
gluon-luci-admin will depend on. gluon-luci-core itself will depends on
gluon-luci-theme, gluon-core and most importantly luci-lib-web. It also
copies a few files from luci-mod-admin-core but leaves out everyting we
do not use.

At a later point I plan to move functionality from luci-lib-web into
this package, too. luci-lib-web contains most parts of luci including
hardcoded templates for CBI, which I intend to replace.

We'll have to revisit translations at a later point after configmode and
expertmode have matured. Texts in this package were pretty inconsistent
anyway so there is no point in keeping translations for random text
fragments.

This makes gluon-autoupdater depend on coreutils-sha512sum when it's not
included in busybox.

Otherwise the enable during image create will throw a few error messages

Do not use 'red' as text color on input fields with errors as the
backgronud color is already red, rendering the value unreadable.

Display the correct hostname on the final page of configmode.
Previously, this page used to simply call luci.sys.hostname() which
would return the current hostname. However, when the configmode changes
the hostname luci.sys.hostname() will not reflect this. This patch
fetches the hostname directly from the UCI system config.

This adds a variable called 'hostname' which may be used in site.conf at
config_mode.msg_reboot and .msg_pubkey.

This reverts commit f5c532a3a923053ab229952bde31da0b0284d8ab.

The reboot page should be delayed a little to give the browser time for
fetching assets (like the stylesheet). This adds a two second delay.
Unfortunately, I couldn't think of a sane way to do this within a luci
controller.

This patch forks the process. The parent will continue rendering the
page for the browser while the child will sleep and then reboot the
device. For this to work reliable the child needs to close stdout before
sleeping so the webserver closes the connection to the browser. This,
again, required a hack as lua does not allow closing std filehandles,
when prevented using luci.reboot() which was calling os.execute() and
that function will not work with stdout closed.