x-plane

The default map is the online OTM map. Many users have their own offline maps like OpenFlightMaps. This results in 2 nasty things:

1. you've always to switch at the beginning of a flight
2. map tiles will be downloaded automatically

Therefore an option to set the default map would be very useful.
Also an option to set a custom online map would be nice.

Right now I believe we can have BLEND_GLASS and GLOBAL_no_blend or GLOBAL_shadow_blend in the header at the same time,
which is wrong.

This is as simple as unit test and a small check in xplane_header.py

Use XSwiftBus::CCommand to allow aircraft labels to be toggled by a keyboard or joystick button. Currently it is only possible via the plugin menu.

We should document these new dataclasses and the new enum. The docs in the code would be fine to copy & paste into the README, with the appropriate formatting.

Seasonalisation? Is that even a word?

Anyway, seasonal support can be improved, particularly snowy winter, by producing new versions of textures with snow incorporated, e.g. snowy roofs.

Unfortunately for the vast majority of the library we can't use the same approach as [Winterizer](https://forums.x-plane.org/index.php?/files/file/51354-winterizer-a-tool-for-snowy-orthophotos/&tab=comments&