allow setting distance and temperature units separately

[jhnc]

GPXSee appears to only allow setting units for distance/speed and temperature together (Imperial, metric, or Nautical).

However, in UK it is normal to use mile units for distance/speed and celsius for temperature.

Please consider splitting the settings so that miles/kilometers/nautical miles and fahrenheit/celsius can be selected independently.

[JH2535]

I'd also like to add that it would be good if we could switch between km/hr and m/s.