workflows: detailed view improvements

* Adds navigation from the Holding Pen details pages
* Adds signals for workflows.
* Updates workflow task viewer.
* Adds classifier/BibClassify task results
1: D290 White spaces around docstring should be trimmed.
1: D400 First line should end with '.', not 'L'
23: D103 Docstring missing
24: D400 First line should end with '.', not 'g'
31: D400 First line should end with '.', not 'g'