Start work on a relabelling collection operation.

I think it needs to be touched up but the basic operation seems to work so far. I think what remains to be done is:

 - Validate uniqueness of identifiers and provide nice messages if they are not unique.
 - Validate that at least the required number of lines are present in the file and provide a nice message if not.
 - Add strict mode to ensure exactly the correct number of lines is added.
 - Find where validation of identifiers happens in the API and apply same validation here - try not to let unsafe identifiers be created.
 - Consider more advanced modes - selecting a column, apply a regex replace, pick two columns for nested lists, etc.... None of this may need to be needed in the first iteration.
 - Consider another mode where a collection is labelled against an existing collection - should that be a separate tool of the same tool.

test-data/new_labels_1.txt

@@ -0,0 +1 @@
+new_i1