invenio-recreate-demo-site: fix default language choice

* Changes CFG_INVENIO_SITE_LANGS default value to "all" so that default
  language choice would be Invenio-version-independent.  Otherwise
  certain languages that are only available on higher versions (say
  "master") would lead to tracebacks on lower versions (say
  "maint-1.1").

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>