BibTasklets: consyn tasklet refactoring

* Adds feed_file parameter to allow the
  conversion 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.

Amended-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
Signed-off-by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>