Improve role management (Participate per workflow)

Instead of having one permission 'Participate in workflows' to enable the roles for all workflows it would be more useful, if that permission could be broken down into the actual existing workflows.

Why? Because having different workflows with different roles causes the permission system and the admin page to get extremely messy.

Lets assume this scenario:

We have 5 workflows - and each workflow requires 5 roles that are only required for a single workflow.

The result is, that the transition page shows 20 "not relevant role checkboxes" for each transition. I have seen websites, where the role / transition system caused the admins to set max_input_vars to 50.000 and this simply can get quite ridiculous and is just not neccessary.

Of course, the admin that actually created all those roles is partially at fault for not doing a better job, but there might be some cases, where it cannot be further optimized.