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 <patrick.oliver.glauner@cern.ch>