OpenStreetMap require an accurate User-Agent or no tiles!

Hi,

OpenStreetMap tiles are currently not loading at all with libosmgpsmap!

A very quick patch changing the user-agent used for downloading tiles. I can't see a need for mocking a browser user-agent now, as all the map sources seem to work.

I've also removed the OSMC map source due to the hostname not seeming to exist anymore!

Thanks,
Andrew