Fix #1541 - skip transit edges in spatial index.

For the graph tiled inspector we added to the spatial index *all* edges, not only street ones. The problem is that some GTFS data do not contain shapes, so for long distance train data (covering a large region such as country/continent-wide networks) the transit edge geometry are single segments of hundred of kilometers. With the new hash grid spatial index we "rasterize" each segment using the envelope only, so in that specific case we end-up rasterizing millions of bins for each segment, which is highly inefficient.

As long as we do not need transit edges in the spatial index we simply skip the transit edges. If they are needed later on, we could improve the hash grid spatial index rasterizing algorithm by for example splitting long segments in small portions of length the bin size.