workflows: definition fetching improvements

* Improves the procedure of getting workflow definition objects
  to be compatible with older workflows that may not exist
  anymore and at the same time be more forgiving.

* Fixes some documentation typos.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
workflows: widget->action name change

* 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 UI
  components.

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

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

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