Bug 15662: String and translatability fix to Label Creator

Bug 15662: String and translatability fix to Label Creator

To test:
1) Go to Tools -> Label Creator -> New label batch
2) Add an item
3) Click 'Remove selected items' button. Confirm message now reads "Please select at least one label to delete."
4) Click 'Remove duplicates' button. Confirm message now reads "Duplicate item(s) removed from batch number X: Y", all in bold.

Signed-off-by: Hector Castro <hector.hecaxmmx@gmail.com>
Rewording Ok for translatability purpose

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Brendan Gallagher brendan@bywatersolutions.com