jsonalchemy: hotfix for fields not always present

* Proposes a patch to fix a little unexpected behaviour
  which happen when a field in the conversion sheet is
  not present in the marcxml. For example email.
  When you will transform the marcxml to dict everything
  will be fine. But when you will convert it back to marc
  xml you will get an infinite loop because befield will
  not find email in the dict. So it will try to eval the
  field email. It will then try to import email, and
  succeed, but because the result contains email it
  will do an infinite loop. In our case email, should
  just be ignored.

Signed-off-by: Guillaume Lastecoueres <guillaume.lastecoueres@cern.ch>
this is holdinpen
workflows: load Celery worker tasks

* Loads the Celery worker tasks so that Invenio Celery wrapper
  can discover the tasks.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
workflows: initial user UI integration

* Kickstarts the user UI integration of Holding Pen by adding
  a new menu item "Your Pending Actions" to the user UI and dashboard.

* Refactors the initial index page of Holding Pen to more nicely show
  pending actions and button to take users to the Holding Pen.

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