base: Test records for Zenodo

* Enables inveniomanage demosite populate with custom xml

* Adds XML with test records for Zenodo.

* NOTE: Before populating DB with demo records from custom xml
  please make sure that BASE_DEMOSITE_RECORDS_FIXTURE
  is set to proper filename (eg. demo_zenodo_record_marc_data.xml)

Signed-off-by: Adrian Pawel Baran <adrian.pawel.baran@cern.ch>
``files = cfg.get('BASE_DEMOSITE_RECORDS_FIXTURE', [])``

This allows to specify more than one file and is more flexible in allowing where the file is located.