Fix map reloading sending malformed query parameters

This patch fixes the periodic map reloading function
sending malformed query parameters, see below:

- `dbris`
- `amp;efa`
- `amp;hafas`

The function now constructs a URLSearchParams object
and appends the serialized parameters to the url instead
of using manual string concatenation.

This would break reloads only for EFA and non ÖBB HAFAS
backends, as the `dbris` parameter was working properly
malformed and ÖBB HAFAS is the default codepath.