Bug 36294: Replace 'book' in system preference descriptions

Bug 36294: Replace 'book' in system preference descriptions

Some system preference descriptions have been updated in order
to replace "books" with items, checkouts or bibliographic records.

To test:

* Check system preference descriptions for following system
  preferences with and without the patch applied:
  * virtualshelves
  * AutoSwitchPatron
  * SyndeticsSeries
  * OPACFineNoRenewals
  * OpacRenewalAllowed
* If they read better than before, sign off :)

Signed-off-by: Laura Escamilla <laura.escamilla@bywatersolutions.com>
Signed-off-by: Emily Lamancusa <emily.lamancusa@montgomerycountymd.gov>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>