workflows: actions 2.0

* Removes the tight coupling to WTForms when designing UI widgets
  for actions in the Holding Pen. Now jinja2 templating can be
  used to render the action.

* Removes the need to dynamically load the actions js files.

* Updates the sample "approval" action to use jinja2 templating
  and simplifies the accompanying js file.

* Removes much unused or unnecessary code including unfinished
  actions and the few defined WTForms fields that are no longer
  used

* Updates the Holding Pen templates to be simpler as a result of
  merging the /actions and /details view into one page (details).

* Updates Holding Pen js files to no longer have hard-coded
  references to the "approval" action.

Co-authored-by: Guillaume Lastecoueres <PX9e@gmx.fr>
Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>