When map is panned, geolocation stops centering

[wbazant]

Closes #518

[ezwelty]

@wbazant The app handles way better, thanks for taking this up.

clicking on the "displaying but not centering" dot re-centers and starts tracking

After panning, at first I expected that it would recenter me when I clicked the track-location button, but instead it stops tracking altogether. Somehow clicking the dot is not as intuitive.

Would it make sense to recenter on first click of the track-location button, and turn off completely if clicked in centering mode? (I think you suggested this single vs double click at some point)

[wbazant]

@ezwelty thanks for reviewing and for suggesting the change! My original double click suggestion was to switch off then center, but center then switch off is still allowing both of them to happen, and I agree that it makes more sense - if the user loses interest in geolocation after panning they'll probably just ignore it, so if they're interacting with it they probably want to re-center.

The change was easy - the same code as for clicking the dot - so I'll just merge it in.