[cmake] Tell to pkg-config where is really the gladys library
Add a getter on the internal graph of nav_graph

Needed to build path planning algorithm
Add a field t to edge structure
Initial implementation of dstar lite algorithm
Document a bit dstar
[test] Fix header of dstar test
cleanup to_string

Thanks to Arnaud D. for the review
[python] decrease path width (5->2px)

Thanks to Cyril R. for the comment.
[visibility] some update