Implement additional Decoding and Tidy

Implement additional bFlags to validate AircraftOnGround, and FS.

Decode Aircraft On Ground from DF0, DF4, DF5, DF16, DF20, and DF21 where
possible.
Flag FS as valid for DF4, DF5, DF20, DF21,

Remove dr and um from the mm structure. They're only used in console
list output mode, so decode them there if required.