Always use current AIRAC, changes/optimizations

[b-faller]

• Always use the last AIRAC with "/latest/base/latest" path.
• Use a less restrictive zoom to allow view of the airport layout.
• Adjust minimum and maximum tile level to prevent fetching of
  unavailable tiles.
• Add download policy for aero tiles as well, since I'm unsure if it is
  picked up.

It's a bit of a mess with quite some changes so feedback is encouraged but I had those changes lying around for some time. 🙂

[AndreGeddert]

Tested this out, works good. Didnt know about the /lastest/base/latest path. Thats very good.
14 days cache time seems reasonable, but maybe a bit too long if AIRACs come every month?
The zoom in is very usefull for ground layout! The zoom out is quite much out, but its ok.

[b-faller]

14 days cache time seems reasonable, but maybe a bit too long if AIRACs come every month?

Could be changed for sure. Ideally we'd be able to flush the cache at an AIRAC expiry date but that's not possible AFAIK so it's a tradeoff how much load we want to put on their servers.

[jonaseberle]

Tested. Works good. Thank you.
I like the higher zoom range.

[LouisTrinczek]

Works as intended

Merging this pull request will fix issue #18

[mol-lux]

Is there hope for this getting merged anytime soon? This fix works, but expecting everyone to dig this far down is... suboptimel :D

Pinging @AmbitiousPilots