BibTasklets: consyn tasklet refactoring.

* Adds feed_file parameter to allow the
  convertion from an atom feed stored in file system.

* Atom feed is deleted only if the tasklet completes
  with no errors.

* Adds to the end of the bibsched log the name of all
  the Exceptions encountered and not dealt properly.

Signed-off-by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>