Change rendering of right borders of the annotations

In the current implementation, the borders of the rectangle representing an annotation on the timeline are placed at the time instants of the “start” of the initial and the final frames of the annotation. This is okay for the initial frame, but may be misleading for the final frame.

The screenshot below illustrates the situation:

The initial frame of the annotation labelled 2 comes immediately after the final frame of the annotation labelled 1. However, there is a gap between the two annotations, which may induce the user to think, erroneously, that there is an image in the gap.

One solution for that would be to always draw the right border of the annotation at the start time of the frame following to the final frame of the annotation in question.