gluon-autoupdater: Always allow forced autoupdate.

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

gluon-alfred: replace announce.sh with lua script

Closes #20

An undocumented feature of uci:get_first() is to cast the returned value
to the same type as the default argument. Thus, supplying a default
value ot type number makes string.format superfluous.

This replaces announce.sh with a lua script of (hopefully) equal
functionality. Using lua generating JSON is much faster than jshn and
allows for greater flexibility.

As we don't have any older gluon versions so far, and hope to be able to do all
upgrades with invariant scripts, remove the code for now.

If we ever see the need to add such upgrade scripts, we can just re-add this.