Fix coincident edge label display

[vincerubinetti]

Currently the edge label is positioned outside/along the line. Let's move it to in the center of the line with a white outline.

This will eliminate the code that determines whether the text is displayed on the "outside" of the curve, which was error prone and complicated.

Several ways to accomplish this. Will test to see which is best.

[vincerubinetti]

I think the performance is too important in this case to actually implement what I said in the original post. As such, changing this issue to "Fix coincident edge label display". I remember seeing a very specific case where the positioning of them is screwed up (but the consequence is just that the text is upside-down, I believe, so considering this an enhancement). Will test various inputs to try to find it, and make sure it can handle anything.