Add ability to "trim" or remove non ski tracking from ski day

If for example I forget to stop carv tracking at the end of the day, it tracks and logs driving vertical, and skews stats for skiing. I have this happen a few times with my Garmin after biking or skiing, but you can “trim” and remove a portion of the start or end of an activity. This might also be useful to remove walking around through a resort mid day. As it appears to log the vertical as well.