installation: legacy snippet configuration support
installation: legacy snippet configuration support

* The commit fec0eb253059b87328b2b61a04d9c6c7f41d131a changed
  the full-text snippet configuration from global per-word to
  per-doctype per-character based (for the v1.1 release series).
  This commit recognises the old style of configuration (the one
  used in v1.0 release series) and warns the user to update
  his/her invenio-local.conf file in case the old style is
  still used.  Thanks to Theodoros Theodoropoulos for reporting
  this problem.

Co-authored-by: Tibor Simko <c7116e45300b163846dc01f3ed02116e3f8ef7a5@cern.ch>

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