RouteService::set_route() when using web-sys unnecessarily serializes/deserializes state to a string

[kellpossible]

When using RouteService::set_route() with web-sys, it serializes the state to a string, and then deserializes it again into a JsValue. I think it should be possible to go directly from the state to JsValue using JsValue::from_serde().

There are other similar instances of this within RouteService.