[Feature] Make/permit arrows (spec. tacked arrows) show on minimap

[jasonhemann]

I think it would be an improvement if the minimap also displayed at least tacked arrows, so that one could quickly jump roughly to use sites rather than having to scroll. I could imagine wanting all the arrows to show also in the minimap, but I could also imagine that being annoying. However, at least the tacked ones could be useful.

[rfindler]

I've pushed two commits so you can see what it looks like. I'm not yet sold, mostly because it seems like a lot of blue and I'm not sure what to do about the arrow heads. If you want to play around with it to make it look nice that'd be great!

This isn't the way it'll get put in there eventually as there's more work to do to cooperate with all the refresh fanciness in that code already but this should be enough to get some idea how it will look and to experiment with ideas to make it look nice.