More work towards getting edge labelling working

Split up geometry graph tests into various more specific tests, because
there is so many of them. One geomgraph test currently fails, all others
are passing.

Refactored lib/geomgraph2/intersector.dart and made a couple of small
changes. Trivial line segments can now not be added to an intersection
info (instead their start coordinate is added

I think its about time to get rid of geomgraph and replace it with
geomgraph2