BibDocFile: revert md5 property patch
BibDocFile: revert md5 property patch

* Reverts md5 property patch 18c013cd7e511cb83d742e70bb0972e426ae0b0e
  that was defining only getter, not setter.  This caused problems
  during recreation of demo site.  (references #1249)

Reported-by: Patrick Glauner <5443b88bc6611431eef05c8ef00b7fee188ca13d@cern.ch>

inveniosoftware/invenio,inveniosoftware/invenio,tiborsimko/invenio,tiborsimko/invenio