[Qt frontend] Show the distance between atoms when two atoms are selected in the "Atoms" view

[yurivict]

It's natural to ask what is the distance between two atoms. Vipster should display the distance (for example under the "Atoms" list) when two atoms are selected.

[sgsaenger]

Thanks for your rigorous testing. Distances, angles and dihedrals are provided by the "Selected Atoms" widget. Any suggestion on how to make this more visible?

[yurivict]

This wasn't obvious. Thanks!

You can make the "Selected Atoms" menu item enabled when 2+ atoms are selected, and disabled when 0 or 1 atoms are selected. It doesn't show anything useful when just one atom is selected anyway.