Automatic fixes before placing a filter

[dabreegster]

In v1, if you try to filter a one-way road, the tool first makes the segment two-way. The first time it does so, it warns the user (and by default, lets them only see that once).

Similarly, the only filter that can be placed on a road with bus routes along it is a bus gate.

Have to rethink the WASM API. Should it be two calls, or should the main 'add filter' call return something indicating an error to prompt the user with? If the user has opted into fixing that kind of problem automatically, does that choice live in the frontend and it silently makes two WASM calls?