Main edit UX

- [x] Change cursor to make it clear what clicking will do
- [x] Adding a filter snaps to nearest road currently, but for one-ways, have to click a road exactly. Both are kind of clunky.
- [x] Deleting filter vs adding can conflict when cursor is over both
- [ ] Road labels seem to prevent the popup for filtering/oneways
- [ ] Try the thick outline style for hover instead of color+opacity
- [x] The edit panel/controls need re-thinking; they're probably worse than the old version
- [x] Basemap + colors / stuff drawn on top aren't as clear as old version
- [x] Warn loudly when a cell becomes disconnected