ed: rewrite the generation of connections
ed: add a default connection of 2 min from a stop point to itself if not provided
routing: do not use an implicit connection of 2 min from a stop point to itself

Connections from a stop point to itself need now to be explicit in the data.

WARNING: import to ed take care to add a connection if there is none, but if
you make your own import, take care of that!
Merge pull request #541 from TeXitoi/connection-to-itself

Connection to itself