Bug 21003: Made Edit keywords more consistent in add_items-step2.tt

Bug 21003: Made Edit keywords more consistent in add_items-step2.tt

When adding a course reserve with a barcode that already exists, the
title, breadcrumbs, and legend of the form all specify that the user is
editing, and not adding, the book.

Test plan:
Same as comment 1

Signed-off-by: Devinim <kohadevinim@devinim.com.tr>
Signed-off-by: Bin Wen <bin.wen@inlibro.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>