Simultaneous track time point position support

[araghon007]

Similar to issue 166 from the old repo (gpxstudio/gpxstudio.github.io#166).
Currently, selecting multiple tracks appends one after the other on the timeline, ignoring the timestamps:


I believe it would be nice for visualization purposes if we could see positions in certain time on both tracks when hovering over the timeline, for example:


also with the possibility to lerp between 2 points on a track if there isn't enough data

I know this is a pretty niche use case, and as such shouldn't be prioritized, but it would be highly appreciated in the future.
I'll try to look for a way of adding this feature myself as well, and if I find a way, I'll send a pull request.
Btw amazing work on the website so far, I only started working with GPX today and this site is easy to find and the most feature rich one I could find that doesn't require a registration.