workflows: widget to action name change

* NOTE Changes the naming of Holding Pen "widgets" to "actions" to
  more clearly distinguish these UI elements from widgets elsewhere
  in Invenio. The name "action" better suits these types of components
  which is representing an action that needs to be taken by operators.

* Renames several files to make use of this new naming strategy.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
workflows: user session in Holding Pen

* Fixes the way the Holding Pen is storing info about the
  current session by actually using the user session and not
  editing the current_app.config.

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