Bug 26718: Rename "reading history" to "checkout history"

Bug 26718: Rename "reading history" to "checkout history"

This changes all occurences of reading history to the more
accurate term 'checokut history' as it was correctly pointed out
that 'reading' doesn't apply to all kind of items available
at the library (audio books, games, etc.)

To test:
- Verify that the term reding history has been replaced by checkout
  history in:
  - System preferences
  - OPAC tab "your checkout history"
  - OPAC tab "your privacy" (switch OpacPrivacy pref first)
  - Staff permission for patron batch anonymization

Signed-off-by: Barbara Johnson  <barbara.johnson@bedfordtx.gov>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>