BibTasklets: APS harvest reloaded

* Refactors the bibtasklet code and migrates lots
  of functionality away from the tasklet and into the apsharvest
  module instead.

* Adds new modules in apsharvest to keep custom errors contained
  as well as refactoring tasklet code into an OO paradigm in
  apsharvest_engine.

* Adds any FTP uploaded files to summary e-mail.

* Updates FTP API in apsharvest_utils by squashing two functions together.

* Improves the documentation in the bst_apsharvest script.

* Makes the final results filename more readable by including the
  dates harvested (if available) or the current date in the name.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>