Bug 9259: Ability to delete a staged file once it has been cleaned

Bug 9259: Ability to delete a staged file once it has been cleaned

To test:
1) Go to Tools -> Staged MARC Management and clean a file. If you have no files to clean, go to 'Stage MARC for import' and upload one to clean following the necessary steps.
2) Confirm that once the file has been cleaned, the Action column now shows a Delete button. Confirm this button only shows for cleaned files.
3) Click the Delete button.
4) Confirm that clicking Cancel exits the pop-up message and does not delete the file.
5) Confirm that clicking OK refreshes the list of staged records and the one you just deleted is no longer on it (has been deleted). You can confirm this by checking for the file in mysql (SELECT * FROM import_batches WHERE import_batch_id = X;)
6) Run prove -v t/db_dependent/ImportBatch.t (have written unit tests for CleanBatch and DeleteBatch)

Sponsored-by: Catalyst IT
Signed-off-by: Liz Rea <liz@catalyst.net.nz>
Catalyst sign off, so needs another one but YAY this is great.

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>