Show pending tasks when we click on "pending tasks"

[jbilcke-hf]

Context

Currently when we generate things, we only display a loading button in the timeline, with no indication of duration, estimated end time, success or error

Moreover if we scroll horizontally, we can quickly lose the segment, making it difficult to track pending tasks

Solution

When we click in the bottom bar on the right, we should display a list of pending tasks (ideally with aprogression bar, or at least an estimate)