An option for notification to display heart rate instead of speed.

[rilling]

For me the current notification that OpenTracks keeps in the notification area contains no useful information: I'm never gonna compete, so I don't care what my speed is. OTH I do care a lot what my current heart rate is, because I have some heart problems. So I would much like prefer for the notification to display the current heart rate.

It would be ideal if the user could set up which parameter he prefers to see in the notification: speed/heart rate/distance/etc. If not, could you at least please make an option to display the heart rate instead of the speed?

Replicated from the original OpenTracks App repository:

OpenTracksApp/OpenTracks#1693