add Footway Area area:highway label

[matkoniecz]

fixes #131

sadly, not tested because I have no idea how to do this #131 (comment)

If this will pass then I will create at least area:highway=cycleway one (area:highway=path is a bit tricky)

[1ec5]

By the way, this preset will already be searchable by “footway” regardless of language, because iD will match tag values: openstreetmap/iD#8869 (comment). If matching keys is also desired, maybe that should be a more general, non-preset-specific feature on the iD side, so other consumers like Overpass turbo can decide not to match keys if it doesn’t make sense for their use case.