Visualize turn restrictions: leftovers

- [ ] When detecting TRs from OSM upfront, filter them out if they're redundant with a one-way. If a user wants to change this, they shouldn't have to take two actions, and the one-way is "stronger" than a TR, since it covers all source roads.
- [ ] Construct a unit test for the above. Also add another unit test based on https://www.openstreetmap.org/relation/15006809, where there's both a oneway and TR, but the TR is not redundant.
- [ ] Consider de-emphasizing or hiding U-turns on dual carriageways. They're implied and probably easily understood by most users, so they just become noise.
- [ ] When hovering on a TR icon, try showing a two-line arrow or using some kind of red/black gradient to show the direction more clearly