Bug 25630: Fix capitalization and terminology for Patrons system preferences

Bug 25630: Fix capitalization and terminology for Patrons system preferences

- Consistent use of 'staff interface'
- Ending punctuation
- Rearranged/rephrased for better readability

To test:
- Verify:
  - patronimages
  - PatronsPerPage (rearranged)
  - PatronQuickAddFields (rearranged)
  - PrefillGuaranteeField (punctuation)
  - borrowerRelationship (punctuation)
  - GDPR_Policy
  - CollapseFieldsPatronAddForm
- read correctly.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>