Add a workflow manager to control next and previous actions

I worked on it this week end a little bit, not completed yet, I'm still on it.

Hey Hakim,

Impressive work on this point !
I progressed in the code review, here is a small summary :

• This module performs alteration on the node table, on my test it generated an error :
  Drupal\Core\Database\DatabaseExceptionWrapper: SQLSTATE[42S22]: Column not found: 1054 Unknown column 'node_field_data.field_forms_steps_id' in 'where clause': SELECT base_table.vid AS vid, base_table.nid AS nid FROM {node} base_table INNER JOIN {node_field_data} node_field_data ON node_field_data.nid = base_table.nid WHERE (node_field_data.field_forms_steps_id IN (:db_condition_placeholder_0)) AND (node_field_data.default_langcode IN (:db_condition_placeholder_1)); Array ( [:db_condition_placeholder_0] => [:db_condition_placeholder_1] => 1 ) in Drupal\Core\Entity\EntityStorageBase->loadByProperties() (line 504 of /var/www/html/web/core/lib/Drupal/Core/Entity/EntityStorageBase.php).
  I had to fully uninstall the module and reinstall it to make it work. As we already have a few people using the module I think we should implement a hook_update_N() to make a proper transition for this branch, what do you think ?
  
• In .module file you are implementing a presave hook to check the uuid presence, I guess it's because you always require one, but it's seems a bit dirty to populate the uuid before the core do. I guess this can lead to some problems with other contribs. Is there no way to delay the operations that requires it to be sure the core has already populated it instead of creating it by ourselves ?
  
• I spotted a bug : when I edit a form step content type, it is not saved.
  
• I'm not fan with the url containing the UUID, is this really mandatory ? I know we discussed to implement a selector to retrieve the entity of previous steps in a future version of the module, but didn't we talked about storing this info in the user storage ?