gluon-config-mode: Corrected grammar

gluon-core: force kernel panic on out of memory

This also adds /lib/gluon/functions/sysctl.sh for setting sysctl options.

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.

In combination with kernel.panic the node will reboot if out of memory.

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.