Modify Feature BySegment. Edition doesn't continue after a vertex is deleted

[miguelbelem]

Some kind of vertex index refresh is needed when one of them is deleted.

[dr-jts]

We're seeing this problem too. Basically BySegment doesn't handle vertex deletion.

It seems like BySegment needs to override handleKeypress. Although perhaps the vertex deletion code in that method should be factored out into a more focussed method (in case other key handlers are added in the future).