Bug 21091: Move add item template JavaScript to a separate file

Bug 21091: Move add item template JavaScript to a separate file

This patch moves the JavaScript in the add item template to separate
files: 1 JS file and 1 include file containing translatable strings.

While moving the JS to cataloging_additem.js I have made some changes to
quiet ESLint warnings (spacing, variable definition).

To test, apply the patch and open the add item page for an existing
record. Test the various JS-driven functionalities:

- Table sorting
- Table column configuration
- Table searching
- Table inline edit/delete links (click anywhere in the table row)
- Add multiple item form show/hide
- Add multiple item warning when adding 100+ items

Signed-off-by: Jose-Mario Monteiro-Santos <jose-mario.monteiro-santos@inLibro.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>