in cases where UUID and adsbx specific uuids differ, there was a bug of
UUID_FILE being set to /run/uuid by adsbx-stats script in
/etc/default/adsbexchange-stats
the json-status script should read from
UUID_FILE=/usr/local/share/adsbexchange/adsbx-uuid
just export ADSBX_UUID in adsbx-stats which then invokes
adsbexchange-json-status.
in there use ADSBX_UUID instead of doing the redirect via the UUID file
cleanup the whole configuration file stuff for adsbx-stats, just
customize json-status a bit
also speed up build as build-essential doesn't need to be installed on
the mlat-client baseimage, it already has it
