If we want to include dive computer names in the undo system,
there should be visual feedback on undo/redo.
This would mean opening the divecomputer dialog, which would
appear quite strange. Therefore, add a tab. This is not ideal,
but consistent with the dive site tab, which probably shouldn't
be there either. In the future, the UI needs some rethinking.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
