Bug 27631: (follow-up) Various corrections

Bug 27631: (follow-up) Various corrections

This patch addresses issues found during QA:

- Double headings (patron details page)
- Inconsistent heading position (check out, patron accounting)
- Missing headings when there is no data (Library EANs, Item search
  fields, MARC modification templates).
- Typo: Z19.50 => Z39.50
- Reword "Classification sources" heading: "Classification
  configuration"

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>