Fixed alignment + aggregation notebooks (paper example)

[LucaMarconato]

Fixed the alignment + aggregation notebook (same example as in the paper).

Before merging the following plot should be fixed (bug in spatialdata-plot):

Expected:

We get:

[LucaMarconato]

I'll report the bugs in dedicated issues in spatialdata-plot, but what is broken is:

• weird double colorbar + legend (proposed fix is 1) to name colorbar/legends so that the user knows what they refer to; 2) to let the user choose if showing the colorbar or not by a colorbar: bool argument; 3) to fix the spacing between them.
• setting a custom cmap for a DataTree object is broken
• in the right plot we wanted to plot the images and then plot shapes on top. The shapes are not shown.

[LucaMarconato]

Not high priority to merge this because I plan to show this in a workshop in 3 weeks, but we should still fix the bugs in spatialdata-plot promptly as they limit usability.