fix editing so you can see timestamp and position while editing

currently i have to export my tracks, then import them to garmin base camp, then save them, then import again into caltopo

the ideal operation would be:

1. Open a recorded track.

2. Move a start slider to when you began hiking.(showing on the map where it is like in garmin base camp).  showing the time stamp like in garmin base camp)

3. Move an end slider to when you reached the car.

4. Click Trim and Save, preserving the GPS timestamps and elevations.