Flown distance

I was not able to issue a pull request
Please add the flown distance in the log analyser, So we do not have to plot the date to google earth to find out how the flown track was long

Start in Mission Planner's log analyser, where flight-track data is processed and presented. Determine how flown distance should be calculated and displayed so users no longer need to plot the track in Google Earth; done means the analyser reports the track distance.

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