deposit: duplicate validator with prod inspirehep

* Queries inspirehep.net to check if a submited publication is
  already in the production db.

Signed-off-by: Kamil Neczaj <kamil.neczaj@cern.ch>
deposit: taskManager rewritten to use deferred objects

Signed-off-by: Kamil Neczaj <kamil.neczaj@cern.ch>
validation chaining
separation of validation function
removed unused arg
validate generalisation