Have a new category of action that enables to put buttons on the create or edit form

It happens many time that we want to have buttons like "save and start the workflow".
For that reason, it should be possible to put some user actions just beside the default save/cancel buttons in the creation/edition layout screen, so as to bind a chain to it that would save the document and do something else... Maybe a new operation is also required here to be able to save the document.

+ make it possible to define the "immediate" element on actions