feat(workflow): add initial state/action registration

introduce `superdesk.workflow` module with `workflow_state` and
`workflow_action` registers

added state field and an example usage for spike (just registration)

not sure about this `include_state` `exclude_state`, ideas?

@akintolga @sivakuna-aap @marwoodandrew @mdhaman 
This should be moved to part of `archive_spike.py` as Spiking and Unspiking of content is done in `archive_spike.py`