Backtrack record every X distance

[kylecorry31]

Rather than recording by time, allow the user to record every ~X distance. This can be done using either the pedometer or with #1719 (speed).

[astewart77]

I like the pedometer idea better than actual feet/meters. I could set Backtrack to my preferred number of steps and leave it that way. Then calibrate the pedometer at the beginning of a hike for the effect of terrain/weather/pack weight on me.