legacy: docextract imports fix
legacy: docextract imports fix

* Fixes import statements after move to new structure.
  (addresses #2210) (PR #2223)

Signed-off-by: Lars Holm Nielsen <7eaffca9f7cd98839b5821d0d23e09ff764b82cd@cern.ch>

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