Common interface for Task models

[mauromsl]

Is your feature request related to a problem? Please describe. It would be useful to develop a common interface for the different task models that we have implemented across all the workflow stages. This would allow us to:

• Fetch open tasks generically: Useful for subscribing for notifications on pending tasks, rendering actions in the dashboard page etc.
  • Manage tasks generically: Would allow certain parts of the system to open/close multiple tasks at once regardles of their type and specifics of the interface (e.g Article.close_workflow_objects)

Describe the solution you'd like A mixin or a multi-table inheritance model that declares a common interface for all task models

Describe alternatives you've considered Not doing this and maintain all the various interfaces that all current task models have, as well as explicitly hunt import all the task models when required

[joemull]

A reminder to re-show Enable digest -- see #2839

[joemull]

Just to note, the University of Essex have mentioned they'd like to see this kind of feature around notifications so they don't have to hunt tasks down in different views.