Automated traffic bollards

New modal filter type with special semantics -- the filter is ignored for residents or drivers with exemptions. The physical implementation could be ANPR (license plate) cameras or some kind of radar key to control a bollard up or down. From the modelling perspective in the tool, it means:

- In the route mode, there's a new checkbox defaulting to off for "resident who can drive through automated traffic bollards". When enabled, these filters are ignored.

And that's all. The shortcut calculation would treat these like any other filter, not allowing traffic past it. This implies that the problematic through-traffic is not caused by the drivers with these exemptions. Likewise, the predict impact mode remains the same -- the changes there reflect wider traffic patterns, not the few people who have this exemption.

Implementation should be fairly simple:

- [ ] Make a filter icon matching the existing dimensions/style in `assets/filters`
- [ ] Find or take a real photo of one with an OK license (like CC0)
- [x] Add the `ModalFilterType` case on the frontend and the `FilterKind` on the backend
- [x] Add the new checkbox to `RouteMode`
- [x] Update the `compareRoute` WASM API
- [x] Update `rebuild_router` to care about both `main_road_penalty` and this new boolean. Plumb through the logic to ignore the filter. When calculating shortcuts or impact, make sure to leave this disabled.

@Kandico, which steps do you feel comfortable doing? The first two design ones are hard for me; I can probably find time soon to handle the rest.