Bibsched: data exchange between tasks

* Tasks now are able to send parameters to the post
  process task (e.g. the record ids processed).

Signed-off-by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>
Websearch: record ids processed are sent to post process task

Signed-off-by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>