[ENHANCEMENT] Combine atom selection and grouping

[MBartkowiakSTFC]

Is your feature request related to a problem? Please describe.
At the moment, atom selection allows the users to pick a subset of atoms on which to perform the analysis. Grouping allows to output the results not per element but per molecule (averaged or summed over atoms in the molecule). However, there are no checks for situations in which the users removes half of one molecule using the selection, which should not be allowed.

Describe the solution you'd like
One solution would be to have the grouping level determine the valid selection options. For example, if molecule grouping is active, the selection options should only allow to select or remove entire molecules and not single atoms.

Describe alternatives you've considered
Any other ideas are welcome.

Additional context
N/A

[oerc0122]

Some tools which enable some form of atom selection off the top of my head:

• Jmol
• Materials Studio -- I think STFC have a license.
• OVITO
• molview