[BUGFIX] Improve l10n_mode config for sys_file_reference

Since the rendering in the Frontend does not merge the values
the mergeIfNotBlank setting is replaced with prefixLangTitle for
the alternative, description and title field.

For the link field the mergeIfNotBlank setting is removed because
a prefix does not make sense there.

Change-Id: I09dfd6d971357ceaeaa08f60057323b3c7e33aa1
Releases: master
Resolves: #59972
Reviewed-on: http://review.typo3.org/32758


Reviewed-by: Frank Nägler <frank.naegler@typo3.org>
Tested-by: Frank Nägler <frank.naegler@typo3.org>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>