Bug 17005: Add checked_in checkouts to REST API response

Bug 17005: Add checked_in checkouts to REST API response

This patch implements parameter 'checked_in' on checkouts endpoint to
enable getting circulation history.

Test plan:
1) Apply the patch and restart plack
2) Use your favorite REST API tester and play with /checkouts endpoint:
    - use it without checked_in parameter
    - use checked_in=1 for getting returned checkouts

Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>