Revert "flights: Use subqueryload() instead of joining everything in one huge query"

This reverts commit a193934410cffca56e1d03c80f688af6bffbfa03.

That did *not* work!!
mapproxy: serve 8-bit PNG files

Reduces file size by over 2/3 with minimal visual impact.

Requires MapProxy 1.6 with Pillow for image processing for suitable
results.