Show time on point edit

[danvk]

Fixes #227. Certainly styling is up for debate here.

I looked into re-keying the height graph by time (rather than distance) or just showing the time of each point on hover. This chart is built using https://github.com/GIScience/Leaflet.Heightgraph which, unfortunately, is unmaintained and impossible to customize in this way.

[pfbreton-perso]

What is the purpose of showing time on waypoints? In my understanding, those handles are typically used to create new tracks, and therefore the statistics on thos points (like time) aren't really available? There might be a whole series of se cases that I am not familiar with - i am interested hearing about them :)

Wouldn't be more useful to see the calculated time all along the graph in the tooltip that is displaying the distance and elevation?

[vcoppe]

Closing this PR because I think it would be better to see this information outside of the edit mode, and for all track points (not just those that act as anchor points for routing). I created a new issue for this.