Small decimal coordinate values are sent to OKAPI in scientific notation

[FriedrichFroebel]

Coordinates like E 000° 00.023 (0.000383 in GPX file) are not serialized correctly (example geocache: https://www.geocaching.com/geocache/GC6T8FW_4587-est-smx). They will be sent in scientific notation (3.83E-4) to the OKAPI in scientific notation, which responds with an error code 400.

We should make sure that these values are serialized correctly, id est we should send 0.000383 in our example. This requires a custom formatter which should be locale-independent (otherwise we get a comma instead of a period as a decimal separator on some systems, for example on German ones).