Scrolling on the sections list updates the preview (without having to click)

@afonsobspinto @zsinnema Could we add the UX like in vfb that allows the user to scroll through the slides using the mouse scroll. So when the user has the mouse pointer on the heatmap and scrolls the mouse, the underlying structure slides changes following the mouse action (i.e. scroll up --> scroll slides towards C1 rostral, scroll down --> scroll slides towards T1 caudal). To avoid slow downs, if the heatmap and/or centroids of multiple populations are toggled on, the computation should wait to trigger until the user has stop scrolling and has settled on a slide (for longer than 300-400 ms)


cc @tarelli