enable/disable identifier based on settings in conf

There is an issue in displaying identifiers in 'editable' search display. Identifiers are always editable regardless of how they are set in the configuration file (multipart_id_numbering). In this fix we solve this issue. Now, the identifier column will be disabled if 'editable' is set to 0 in the configuration file.  
We also disable identifier column if identifier is a composite element, because it is not clear how the update operation will be performed for its composing elements.