Bug 11559: (followup) Prevent saving item tags, fix other issues

Bug 11559: (followup) Prevent saving item tags, fix other issues

This fixes the following issues:
  * Spaces are now allowed in indicators
  * Shift-Enter is available to insert a newline if needed
  * Item tags, if present, will prevent saving (as they are not correctly
    processed by the backend)
  * biblionumber tags (999 in MARC21) will be stripped before the record
    is saved to Koha, to prevent their modification

Signed-off-by: Nick Clemens <nick@quecheelibrary.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>