Add coherence to sections

__Add coherence in journey' sections__

We want to have coherence between the from (to) of a section and the from (to) of the request.
It also adds coherence between the to (from) of the streetnetwork section and the  from(to) of the first (last) public transport section. Therefore the to(from) of the streetnetwork section is now a stop_point, you still have the adress of the stop point in the place.

We also don't really know from where we start when we start from a area (a stop_area or an admin), thus we added a crow_fly section which starts from the centroid of this area and goes to the first stop_point of the first pt_section.