errors: InvalidOperationError 403 code setting
errors: InvalidOperationError 403 code setting

* Sets 403 as code for InvalidOperationError.
  (closes inveniosoftware/invenio-deposit#91)

Signed-off-by: Leonardo Rossi <5460ec99b71a72e7693c4088b5c2585e76e1c857@cern.ch>

inveniosoftware/invenio-files-rest,inveniosoftware/invenio-files-rest