Added a function to add additional node in unconnected lanes.
Solved some bugs.

Added functions to update all the references when a new road is created.

  * A function to get the closes node to a point.
  * A function to get the set of closest points to a point.

Found a bug (not yet solved): The contact point information is needed when linking junction roads.

Completed the feature to copy the whole structure and update the references.

Road nodes from diferent roads at the same location are fused.
Road nodes can belong to multiple lanes: each has a vector of parent lanes and geometries.

Added support to link road segments.