Move aeroway=terminal back to z13

[Prince-Kassad]

This would partially revert #3467.

Airports, especially huge airports, look really strange now that terminals (which are usually very large structures) are gone from z13.

Cf. Frankfurt Airport: https://www.openstreetmap.org/#map=13/50.0549/8.5796
New York-JFK: https://www.openstreetmap.org/#map=13/40.6670/-73.7783
Rome-Fiumicino: https://www.openstreetmap.org/#map=13/41.8136/12.3047

I think we can live with creating a special exception for terminals only because they're not very common.

[jeisenbe]

Would this also apply to other transportation terminals, e.g. train stations?

[Prince-Kassad]

I've picked airport terminals specifically due to their size. I don't think train stations are large enough to warrant rendering on z13. Even very large train stations like Frankfurt or Leipzig barely stand out and as long as we have no way to differentiate between large and small train stations (or even former train stations, since building=train_station does not tell you whether the train station is still in service) we couldn't prevent tiny buildings from suddenly showing up on z13 for no particular reason.

[jeisenbe]

Small airports have small terminals. This is especially true here in the tropics, where the Mercator projection makes our terminals look even smaller. See e.g.: Wamena Airport Terminal - it's the biggest building in the city and a newly-built passenger terminal for a regional airport, but still quite small on z13. I suspect many European train stations are much larger.