BibFormat: improve Dublin Core output

• Adds record URL to <dc:identifier> element.

• Adds 037$a AND 088$a to <dc:identifier> element. (closes #320)

• Adds OAI identifier (CFG_OAI_ID_FIELD) to <dc:identifier> element.

• Adds 0247_a to <dc:identifier> element when 0247_2 is "doi". (closes #1213)

• Adds 260$b to <dc:publisher> element.

• Display corporate author (110a/710a) when author is not available (100a/700a).

• Updates <dc:date> element to fetch data from bfe_date. Fall back to record creation date if no value found.

• Removes link to files (8564_u).

Signed-off-by: Jerome Caffaro <jerome.caffaro@cern.ch>
Tested-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>