Bug 18804: (bugs 16400,11088 follow-up) Update the "save category" elt selector

Bug 18804: (bugs 16400,11088 follow-up) Update the "save category" elt selector

With bug 11088 and bug 16400 the submit node switched from:
  <input type="submit" name="save" onclick="return check_form_borrowers();" value="Save" />
to:
  <button type="submit" name="save" onclick="return check_form_borrowers">
then finally to:
  <button class="btn btn-small" id="saverecord" type="submit" name="save" onclick="return check_form_borrowers();">

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Lee Jamison <ldjamison@marywood.edu>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
(cherry picked from commit 08ab41aa9825e48f6321a90bf0bef09b572d4000)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>