Make the LSJON importing ordered
Make the LJSON import use PointGraph

Create a pointgraph if there is valid connectivity
information
Reorder the labels

Keep the order stable so that PTS to LJSON and back works
properly. The order MUST be maintained to make sure that the
underlying pointcloud maps back and forth
Update landmark.py
Update landmark.py
Merge pull request #439 from patricksnape/labelling_fixes

Labelling fixes