TODO
✓ add rect inside slot to bind removeSlot() on click / or just use dblclick.
✓ add button to 'buils auto' all slots.
- find a way to 'scroll' horizontally when too many items on Y axis to be visible.
✓ augment a slot from the left properly.
✓ when dragging quickly to another slot, 'stick' it to the slot instead of let large space between them.
✓ when add a slot, if not visible, extend viewport to view it.
✓ added slots failed when dragged and could overlap others..
✓ move startDateAll and update all graph (item with prop startAfter instead of start).
✓ adapt slot height compared to Y items number.
✓ allow move on x axis by dragging on graph.
✓ improve minute display on x axis (more point+text).
✓ add new slot for specific Y item > if already line add to it else create new line (update y axis).
✓ have current slot highlighted with border and infos elsewhere with NAME/START/STOP and btnRemove.