Clean up StreetVertexIndexService interface and implementation

1) There were a number of old-style methods dangling from my last refactor of StreetVertexIndexService - for example getClosestVertex(Coordinate). I've deleted these methods, using GenericLocation over Coordinate and I've fixed all tests and callers.
2) LocationObservation and GenericLocation are somewhat redundant, so I added an optional heading variable to GenericLocation and deleted LocationObservation as per issue 1014 https://github.com/openplans/OpenTripPlanner/issues/1014.

As usual, everything builds and all tests pass.
Avi