BibWorkflow: API updates
BibWorkflow: API updates

* The way run a workflow in a task queue has changed from a
  task_queue parameter into seperate "delayed" functions, such
  as start_delayed() or continue_oai_delayed().

* Adds custom kwargs to be passed to all workflow API functions
  that will be put into the workflow engine's extra_data column.
  This allows one to access this data from the workflow tasks.

* Documentation improved and corrected overall. Especially in
  bibworkflow_api.

* Updated worker plugins and unit tests to reflect these new
  changes.

* Renames several functions from camelCase to underscore_case.

* Renames Holding Pen template files from bibholdingpen_* to
  bibworkflow_* as well as other restructu.

* Adds a custom exception in bibworkflow_worker_engine instead
  of raising ValueError.

* Changes worker API names.

* Removes references to external_save as it is no longer used.

* Various fixes to the Holding Pen, improving PEP8 etc.

* Fixes many kwalitee issues.

* Adds Redis backend functionality, by Wojciech Ziolek.

Co-authored-by: Wojciech Ziolek <2bd479edd77331d6ea0c37f5ad23417ada968d1b@cern.ch>

inveniosoftware/invenio-celery,tiborsimko/invenio-celery,tiborsimko/invenio-celery,inveniosoftware/invenio-celery