Bug 33864: Better handling of confirmation button

Bug 33864: Better handling of confirmation button

This patch corrects the behavior of the 'Confirm' button on the three
possible scenarios regarding item creation.

Ordering:
- 'Confirm' disabled, only gets enabled if quantity > 0

Receiving:
- Quantity gets locked (only changeable when creating items)
- 'Confirm' disabled, only gets enabled if quantity > 0

Cataloguing:
- It now defaults to 1
- 'Confirm' enabled by default (because of 1) if quantity is set to 0,
  it gets disabled.

To test:
1. Verify the described behavior with the sample orders for the previous
   patch.
=> SUCCESS: It does the job!

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Andrew Nugged <nugged@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>