Bug 25630: Fix capitalization and terminology for Acquisitions and Tools system prefe...

Bug 25630: Fix capitalization and terminology for Acquisitions and Tools system preferences

- Adds some ending punctuation
- Fixes capitalization
- Consistent use of "staff interface"

To test:
- Verify:
  - NewsAuthorDisplay
  - EmailPurchaseSuggestions
  - UseACQFrameworkForBiblioRecords
  - AcqItemSetSubfieldsWhenReceived
  - AcqItemSetSubfieldsWhenReceiptIsCancelled
  - OrderPriceRounding
- read correctly.

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