Navigate to start/end of a tracklet

[xulman]

Given the current Menu:

I propose to add two more "hot spots" on a track:

• Select Tracklet Downward
• Select Tracklet Upward
• Navigate to Tracklet start
• Navigate to Tracklet end

(the latter two could also be: Tracklet mother and Tracklet daughter... not perhaps super clear on the first look, but I believe user will find the difference)

They complement "in-between" the current special targets:

• the intermediate previous/consecutive spot
  • to where one can select or navigate
  • which jumps maximally over one division (to the very first daughter spot)
• here the new thing
  • can select and navigate
  • isn't jumping over division points
• and the very beginning(root) / end(all leafs)
  • to where one can only select
  • which jumps over divisions