Add volume in Å^3 in the cell tab

[superstar54]

Add the information in the last line of the widget.

Note: it should depending on the periodicity!
xyz -> Cell volume (ang^3)
xy -> Cell area (ang^2)
x -> Cell length (and)
(for 0D, show nothing!)

Note that StructureData already has a function to return both the dimensionality and the correct value (with the correct units): https://github.com/aiidateam/aiida-core/blob/779cc29d8a47eddabdf9b274d7fa711220ee1aa9/src/aiida/orm/nodes/data/structure.py#L772