gluon-autoupdater: depend on sha512sum

This makes gluon-autoupdater depend on coreutils-sha512sum when it's not
included in busybox.
gluon-luci-admin: remove translation support

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.
gluon-luci-core: replacing luci-mod-admin-core

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.
gluon-autoupdater: enable by default only if GLUON_BRANCH is set, set default branch accordingly
gluon-luci-autoupdater: Fix typo
Merge pull request #18 from sargon/master

gluon-luci-autoupdater: Fix typo
gluon-status-page: show model
gluon-config-mode: remove bind mounts
gluon-config-mode: simplify dnsmasq command, remove sleep after network setup
gluon-config-mode: don't let UCI_CONFIG_DIR leak to the telnet environment etc.
gluon-core: force kernel panic on out of memory

In combination with kernel.panic the node will reboot if out of memory.
gluon-luci-admin: remove reboot feature

Configmode should be exited by using the wizard instead.
gluon-luci-admin: fix firmware upgrade feature
gluon-luci-admin: remove backup/restore
gluon-autoupdater: drop caches before upgrade

This will free about 5 to 12 MB of RAM even on lightly used devices
yielding plenty of RAM for autoupdate to succeed.
gluon-luci-admin: system.lua -> upgrade.lua
gluon-luci-admin: remove unused function
gluon-luci-admin: replace overview with ssh/pass

Various changes and moving stuff around.
gluon-luci-autoupdater: use expertmode template
gluon-luci-admin: expertmode texts translated