How to handle a greater variety of LandmarkTypes

[chebizarro]

The present implementation defines LandmarkType as an enum. While this is efficient for the current navigation algorithm, it will need to be expanded.

https://github.com/ReferencePointNavigation/ProtoBuf/blob/395e8278485ef50d171ffd390641189d106a4335/proto3/LandmarkProto.proto#L25

One suggestion would be to create a new class/message LandmarkType with a property that is more reflective of the nature of the Landmark i.e. obstacle, passagway etc.