Bug 28443: Terminology: Issuing should be Checking out

Bug 28443: Terminology: Issuing should be Checking out

This patch modifies the title element of the batch checkout page so that
it uses the phrase "Batch check out" instead of "Issuing."

To test, apply the patch and enable BatchCheckouts system preference.

- Open a patron for checkout who has a category included in the
  BatchCheckoutsValidCategories system preference.
- Click the "Batch check out" tab and confirm that the page's title is
  correct.

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