Cargo SQL overhaul

The SQL for retrieving a pilot’s cargo stats (tons occupied, available
and the cargo meter) has been rewritten to include mission cargo and
overall work better.
Quick fix to cargo SQL

Ran into parameter availability issues on $pilot->getUserPilot().
Should be corrected now.
Also updated $pilot->getPilotCargoStats to allow manual specification
of a pilot ID. Futureproofiing!
Mission deliveries

Deliveries now work and payout properly.

Caught a nasty bug with the cargo SQL where it was returning NULL
values if it couldn’t find any cargo. Now returns 0s
Yarr

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