Exterior visual updates

Wheel chocks

Use the book to set and remove chocks.
You can only set them when plane is stopped. As soon as the speed is not null, they will be automaticaly removed.

Tie downs

Use the book to set and remove tie downs.
You can only set them when plane is stopped. As soon as the speed is not null, they will be automaticaly removed.

Covers

Use the book to set and remove pitot and cowling cover.
You can only set them when plane and engine are stopped. As soon as the engine starts, they will be automaticaly removed.