CI4: Item CSV Import Broken

[objecttothis]

When clicking the download link for the items csv import file it routes to 'public/items/generate_csv_file' and results in a 404 error. This will be a fairly easy fix of renaming the function in the controller and the view so the auto routing works properly. After that we need to test to make sure that the template is generated correctly. Once done we need to test that imports work properly with both new items and existing items.

[objecttothis]

I've pushed several commits to help with some deprecation warnings and tested. This seems to be working now, so I'll close it. Someone can re-open it if we find further bugs.