The older busybox-based wget erroneously accepted URLs without protocol.
Add validator to avoid building firmwares with broken autoupdates.

Some files have received some additional refactoring.

Fixes #1043

We also make use of the boolean support of simple-uci to make scripts
clearer.

Avoid commiting configs inbetween to decrease number of flash writes.

Fixes #714.

gluon-announced and gluon-announce are merged to gluon-respondd.

Moving the scripts to a common directory not only vastly simplifies the
zzz-gluon-upgrade script, but also allows to define an ordering of such
scripts across packages.

gluon-autoupdater: unconditionally perform an update 5 minutes after boot when the whole PRIORITY delay has passed

The probability field is removed, updates are performed once per night between
04:00 and 05:00.

All announce.d scripts have been moved to /lib/gluon/announce/announce.d
The script /lib/gluon/announce/announce.lua will collect all information
and output json.

Closes #31

This also fixes the type of a few fields which were strings instead of numbers.

On nodes with autoupdate disabled the cmdline parameter '-f' has no
effect. But using the autoupdater for manual updates is quite handy.

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

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

This way we have a kind of load balancing among the mirrors.