JAL-1476: warn user when no columns available to compute structure superposition
When a 'view all structures' or 'Align in Jmol' operation is applied to a set of structures which have no aligned residues in any associated views, then the structure superposition process fails but no indication of what went wrong is reported to the user.
A dialog box (or status bar notification) should be shown to tell the user that the superposition couldn't be performed due to the lack of aligned residues.
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Issues Raised From Comments