refactors all airfield interfaces and types/structs moving them to their
own airfield pkg (was in common). this is part of the refactoring effort
to get rid of common.
Coverage remained the same at 100.0% when pulling 2b52b813a16ffe482d126fa870bb05d700f1a80f on refactor/airfield into 6bd043423ad2f234d8aa44121939ac58fabe8571 on master.
refactors all airfield interfaces and types/structs moving them to their own airfield pkg (was in common). this is part of the refactoring effort to get rid of common.
Implements #69.